program main

!*****************************************************************************80
!
!! MAIN is the main program for TRIANGULATION_TRIANGLE_NEIGHBORS.
!
!  Discussion:
!
!    TRIANGULATION_TRIANGLE_NEIGHBORS determines the neighbor triangles 
!    of each triangle in a triangulation.
!
!    The user supplies a node file and a triangle file, containing
!    the coordinates of the nodes, and the indices of the nodes that
!    make up each triangle.  Either 3-node or 6-node triangles may
!    be used.
!
!    The program reads the node and triangle data, computes the triangle
!    neighbor information, and writes it to a file.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    03 July 2008
!
!  Author:
!
!    John Burkardt
!
!  Usage:
!
!    triangulation_triangle_neighbors node_file triangle_file
!
  implicit none

  integer ( kind = 4 ) arg_num
  integer ( kind = 4 ) dim_num
  logical header
  integer ( kind = 4 ) i
  integer ( kind = 4 ) iarg
  integer ( kind = 4 ) iargc
  character ( len = 256 ) :: input_node_filename = ' '
  character ( len = 256 ) :: input_triangulation_filename = ' '
  integer ( kind = 4 ) j
  integer ( kind = 4 ) node
  integer ( kind = 4 ) node_num
  real    ( kind = 8 ), allocatable, dimension ( :, : ) :: node_xy
  character ( len = 256 ) :: output_tneighbor_filename = ' '
  integer ( kind = 4 ), allocatable, dimension ( :, : ) :: triangle_neighbor
  integer ( kind = 4 ), allocatable, dimension ( :, : ) :: triangle_node
  integer ( kind = 4 ) triangle_num
  integer ( kind = 4 ) triangle_order

  call timestamp ( )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'TRIANGULATION_TRIANGLE_NEIGHBORS'
  write ( *, '(a)' ) '  FORTRAN90 version'
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Read a node dataset of NODE_NUM points in 2 dimensions.'
  write ( *, '(a)' ) '  Read an associated triangulation dataset of '
  write ( *, '(a)' ) '  TRIANGLE_NUM triangles using 3 or 6 nodes.'
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  For each triangle, determine the indices of the'
  write ( *, '(a)' ) '  triangles opposite vertices 1, 2 and 3.'
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Write this triangle neighbor data to files.'
!
!  Get the number of command line arguments.
!
  arg_num = iargc ( )
!
!  If at least one command line argument, it's the node file name.
!
  if ( 1 <= arg_num ) then

    iarg = 1
    call getarg ( iarg, input_node_filename )

  else

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'TRIANGULATION_TRIANGLE_NEIGHBORS:'
    write ( *, '(a)' ) '  Please enter the name of the node file.'

    read ( *, '(a)' ) input_node_filename

  end if
!
!  If at least two command line arguments, the second is the triangulation file.
!
  if ( 2 <= arg_num ) then

    iarg = 2
    call getarg ( iarg, input_triangulation_filename )

  else

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'TRIANGULATION_TRIANGLE_NEIGHBORS:'
    write ( *, '(a)' ) '  Please enter the name of the triangulation file.'

    read ( *, '(a)' ) input_triangulation_filename

  end if
!
!  Read the node data.
!
  call dtable_header_read (  input_node_filename, dim_num, node_num )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Read the header of "' &
    // trim ( input_node_filename ) //'".'
  write ( *, '(a)' ) ' '
  write ( *, '(a,i8)' ) '  Spatial dimension DIM_NUM = ', dim_num
  write ( *, '(a,i8)' ) '  Number of nodes NODE_NUM  = ', node_num

  allocate ( node_xy(1:dim_num,1:node_num) )

  call dtable_data_read ( input_node_filename, dim_num, node_num, node_xy )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Read the data in "' &
    // trim ( input_node_filename ) //'".'

  call r8mat_transpose_print_some ( dim_num, node_num, node_xy, 1, 1, &
    dim_num, 5, '  Coordinates of first 5 nodes:' )
!
!  Read the triangulation data.
!
  call itable_header_read (  input_triangulation_filename, triangle_order, &
    triangle_num )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Read the header of "' &
    // trim ( input_triangulation_filename ) //'".'
  write ( *, '(a)' ) ' '
  write ( *, '(a,i8)' ) '  Triangle order TRIANGLE_ORDER = ', triangle_order
  write ( *, '(a,i8)' ) '  Number of triangles TRIANGLE_NUM  = ', triangle_num

  if ( triangle_order /= 3 .and. triangle_order /= 6 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'TRIANGULATION_TRIANGLE_NEIGHBORS - Fatal error!'
    write ( *, '(a)' ) '  This program can only handle triangulations'
    write ( *, '(a)' ) '  of orders 3 and 6.'
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  The input triangulation seems to have'
    write ( *, '(a,i8)' ) '  order = ', triangle_order
    stop
  end if

  allocate ( triangle_node(1:triangle_order,1:triangle_num) )

  call itable_data_read ( input_triangulation_filename, triangle_order, &
    triangle_num, triangle_node )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Read the data in "' &
    // trim ( input_triangulation_filename ) //'".'

  call i4mat_transpose_print_some ( triangle_order, triangle_num, &
    triangle_node, 1, 1, triangle_order, 5, '  First 5 triangles:' )
!
!  Create the triangle neighbor array.
!
  allocate ( triangle_neighbor(1:3,1:triangle_num) )

  if ( triangle_order == 3 ) then

    call triangulation_order3_neighbor_triangles ( triangle_num, &
      triangle_node, triangle_neighbor )

  else if ( triangle_order == 6 ) then

    call triangulation_order6_neighbor_triangles ( triangle_num, &
      triangle_node, triangle_neighbor )

  end if
!
!  Write out the triangle neighbor file.
!
  output_tneighbor_filename = input_triangulation_filename
  call file_name_ext_swap ( output_tneighbor_filename, 'tneighbor.txt' )

  header = .false.
  call itable_write ( output_tneighbor_filename, 3, triangle_num, &
    triangle_neighbor, header )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Created the triangle neighbor file "' &
    // trim ( output_tneighbor_filename ) //'".'
!
!  Deallocate memory.
!
  deallocate ( node_xy )
  deallocate ( triangle_neighbor )
  deallocate ( triangle_node )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'TRIANGULATION_TRIANGLE_NEIGHBORS:'
  write ( *, '(a)' ) '  Normal end of execution.'

  write ( *, '(a)' ) ' '
  call timestamp ( )

  stop
end
subroutine ch_cap ( c )

!*****************************************************************************80
!
!! CH_CAP capitalizes a single character.
!
!  Modified:
!
!    19 July 1998
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input/output, character C, the character to capitalize.
!
  implicit none

  character c
  integer ( kind = 4 ) itemp

  itemp = ichar ( c )

  if ( 97 <= itemp .and. itemp <= 122 ) then
    c = char ( itemp - 32 )
  end if

  return
end
function ch_eqi ( c1, c2 )

!*****************************************************************************80
!
!! CH_EQI is a case insensitive comparison of two characters for equality.
!
!  Example:
!
!    CH_EQI ( 'A', 'a' ) is .TRUE.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    28 July 2000
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character C1, C2, the characters to compare.
!
!    Output, logical CH_EQI, the result of the comparison.
!
  implicit none

  logical ch_eqi
  character c1
  character c1_cap
  character c2
  character c2_cap

  c1_cap = c1
  c2_cap = c2

  call ch_cap ( c1_cap )
  call ch_cap ( c2_cap )

  if ( c1_cap == c2_cap ) then
    ch_eqi = .true.
  else
    ch_eqi = .false.
  end if

  return
end
subroutine ch_to_digit ( c, digit )

!*****************************************************************************80
!
!! CH_TO_DIGIT returns the integer ( kind = 4 ) value of a base 10 digit.
!
!  Example:
!
!     C   DIGIT
!    ---  -----
!    '0'    0
!    '1'    1
!    ...  ...
!    '9'    9
!    ' '    0
!    'X'   -1
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    04 August 1999
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character C, the decimal digit, '0' through '9' or blank
!    are legal.
!
!    Output, integer ( kind = 4 ) DIGIT, the corresponding integer ( kind = 4 ) value.  If C was
!    'illegal', then DIGIT is -1.
!
  implicit none

  character c
  integer ( kind = 4 ) digit

  if ( lge ( c, '0' ) .and. lle ( c, '9' ) ) then

    digit = ichar ( c ) - 48

  else if ( c == ' ' ) then

    digit = 0

  else

    digit = -1

  end if

  return
end
subroutine dtable_data_read ( input_filename, m, n, table )

!*****************************************************************************80
!
!! DTABLE_DATA_READ reads data from a double precision table file.
!
!  Discussion:
!
!    The file may contain more than N points, but this routine will
!    return after reading N of them.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    26 January 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the input file.
!
!    Input, integer ( kind = 4 ) M, the spatial dimension.
!
!    Input, integer ( kind = 4 ) N, the number of points.
!
!    Output, real ( kind = 8 ) TABLE(M,N), the table data.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) ierror
  character ( len = * ) input_filename
  integer ( kind = 4 ) input_status
  integer ( kind = 4 ) input_unit
  integer ( kind = 4 ) j
  character ( len = 255 ) line
  real ( kind = 8 ) table(m,n)
  real ( kind = 8 ) x(m)

  ierror = 0

  call get_unit ( input_unit )

  open ( unit = input_unit, file = input_filename, status = 'old', &
    iostat = input_status )

  if ( input_status /= 0 ) then
    ierror = 1
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'DTABLE_DATA_READ - Fatal error!'
    write ( *, '(a)' ) '  Could not open the input file: ' // &
      trim ( input_filename )
    stop
  end if

  j = 0

  do while ( j < n )

    read ( input_unit, '(a)', iostat = input_status ) line

    if ( input_status /= 0 ) then
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'DTABLE_DATA_READ - Fatal error!'
      write ( *, '(a)' ) '  Error while reading lines of data.'
      write ( *, '(a,i8)' ) '  Number of values expected per line M = ', m
      write ( *, '(a,i8)' ) '  Number of data lines read, J =         ', j
      write ( *, '(a,i8)' ) '  Number of data lines needed, N =       ', n
      stop
    end if

    if ( line(1:1) == '#' .or. len_trim ( line ) == 0 ) then
      cycle
    end if

    call s_to_r8vec ( line, m, x, ierror )

    if ( ierror /= 0 ) then
      cycle
    end if

    j = j + 1

    table(1:m,j) = x(1:m)

  end do

  close ( unit = input_unit )

  return
end
subroutine dtable_header_read ( input_filename, m, n )

!*****************************************************************************80
!
!! DTABLE_HEADER_READ reads the header from a double precision table file.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    07 September 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the input file.
!
!    Output, integer ( kind = 4 ) M, spatial dimension.
!
!    Output, integer ( kind = 4 ) N, the number of points. 
!
  implicit none

  character ( len = * ) input_filename
  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  call file_column_count ( input_filename, m )

  if ( m <= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'DTABLE_HEADER_READ - Fatal error!'
    write ( *, '(a)' ) '  There was some kind of I/O problem while trying'
    write ( *, '(a)' ) '  to count the number of data columns in'
    write ( *, '(a)' ) '  the file "' // trim ( input_filename ) // '".'
    stop
  end if

  call file_row_count ( input_filename, n )

  if ( n <= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'DTABLE_HEADER_READ - Fatal error!'
    write ( *, '(a)' ) '  There was some kind of I/O problem while trying'
    write ( *, '(a)' ) '  to count the number of data rows in'
    write ( *, '(a)' ) '  the file "' // trim ( input_filename ) // '".'
    stop
  end if

  return
end
subroutine file_column_count ( input_filename, column_num )

!*****************************************************************************80
!
!! FILE_COLUMN_COUNT counts the number of columns in the first line of a file.
!
!  Discussion:
!
!    The file is assumed to be a simple text file.
!
!    Most lines of the file is presumed to consist of COLUMN_NUM words,
!    separated by spaces.  There may also be some blank lines, and some 
!    comment lines,
!    which have a "#" in column 1.
!
!    The routine tries to find the first non-comment non-blank line and
!    counts the number of words in that line.
!
!    If all lines are blanks or comments, it goes back and tries to analyze
!    a comment line.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    21 June 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the file.
!
!    Output, integer ( kind = 4 ) COLUMN_NUM, the number of columns in the file.
!
  implicit none

  integer ( kind = 4 ) column_num
  logical got_one
  character ( len = * ) input_filename
  integer ( kind = 4 ) input_status
  integer ( kind = 4 ) input_unit
  character ( len = 256 ) line
!
!  Open the file.
!
  call get_unit ( input_unit )

  open ( unit = input_unit, file = input_filename, status = 'old', &
    form = 'formatted', access = 'sequential', iostat = input_status )

  if ( input_status /= 0 ) then
    column_num = -1
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'FILE_COLUMN_COUNT - Fatal error!'
    write ( *, '(a)' ) '  Could not open the file:'
    write ( *, '(a)' ) '    ' // trim ( input_filename )
    return
  end if
!
!  Read one line, but skip blank lines and comment lines.
!
  got_one = .false.

  do

    read ( input_unit, '(a)', iostat = input_status ) line

    if ( input_status /= 0 ) then
      exit
    end if

    if ( len_trim ( line ) == 0 ) then
      cycle
    end if

    if ( line(1:1) == '#' ) then
      cycle
    end if

    got_one = .true.
    exit

  end do

  if ( .not. got_one ) then

    rewind ( input_unit )

    do

      read ( input_unit, '(a)', iostat = input_status ) line

      if ( input_status /= 0 ) then
        exit
      end if

      if ( len_trim ( line ) == 0 ) then
        cycle
      end if

      got_one = .true.
      exit

    end do

  end if

  close ( unit = input_unit )

  if ( .not. got_one ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'FILE_COLUMN_COUNT - Warning!'
    write ( *, '(a)' ) '  The file does not seem to contain any data.'
    column_num = -1
    return
  end if

  call s_word_count ( line, column_num )

  return
end
subroutine file_name_ext_get ( file_name, i, j )

!*****************************************************************************80
!
!! FILE_NAME_EXT_GET determines the "extension" of a file name.
!
!  Discussion:
!
!    The "extension" of a filename is the string of characters
!    that appears after the LAST period in the name.  A file
!    with no period, or with a period as the last character
!    in the name, has a "null" extension.
!
!    Blanks are unusual in filenames.  This routine ignores all
!    trailing blanks, but will treat initial or internal blanks
!    as regular characters acceptable in a file name.
!
!  Example:
!
!    FILE_NAME   I  J
!
!    bob.for     4  7
!    N.B.C.D     6  7
!    Naomi.      6  6
!    Arthur     -1 -1
!    .com        1  1
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    17 July 1998
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) FILE_NAME, a file name to be examined.
!
!    Output, integer ( kind = 4 ) I, J, the indices of the first and last characters
!    in the file extension.
!
!    If no period occurs in FILE_NAME, then
!      I = J = -1;
!    Otherwise,
!      I is the position of the LAST period in FILE_NAME, and J is the
!      position of the last nonblank character following the period.
!
  implicit none

  character ( len = * ) file_name
  integer ( kind = 4 ) i
  integer ( kind = 4 ) j
  integer ( kind = 4 ) s_index_last_c

  i = s_index_last_c ( file_name, '.' )

  if ( i == -1 ) then

    j = -1

  else

    j = len_trim ( file_name )

  end if

  return
end
subroutine file_name_ext_swap ( file_name, ext )

!*****************************************************************************80
!
!! FILE_NAME_EXT_SWAP replaces the current "extension" of a file name.
!
!  Discussion:
!
!    The "extension" of a filename is the string of characters
!    that appears after the LAST period in the name.  A file
!    with no period, or with a period as the last character
!    in the name, has a "null" extension.
!
!  Example:
!
!          Input           Output
!    ================     =========
!    FILE_NAME    EXT     FILE_NAME
!
!    bob.for      obj     bob.obj
!    bob.bob.bob  txt     bob.bob.txt
!    bob          yak     bob.yak
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    09 August 1999
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input/output, character ( len = * ) FILE_NAME, a file name.
!    On output, the extension of the file has been changed.
!
!    Input, character ( len = * ) EXT, the extension to be used on the output
!    copy of FILE_NAME, replacing the current extension if any.
!
  implicit none

  character ( len = * ) ext
  character ( len = * ) file_name
  integer ( kind = 4 ) i
  integer ( kind = 4 ) j
  integer ( kind = 4 ) len_max
  integer ( kind = 4 ) len_name

  len_max = len ( file_name )
  len_name = len_trim ( file_name )

  call file_name_ext_get ( file_name, i, j )

  if ( i == -1 ) then

    if ( len_max < len_name + 1 ) then
      return
    end if

    len_name = len_name + 1
    file_name(len_name:len_name) = '.'
    i = len_name + 1

  else

    i = i + 1
    file_name(i:j) = ' '

  end if

  file_name(i:) = ext

  return
end
subroutine file_row_count ( input_filename, row_num )

!*****************************************************************************80
!
!! FILE_ROW_COUNT counts the number of row records in a file.
!
!  Discussion:
!
!    It does not count lines that are blank, or that begin with a
!    comment symbol '#'.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    06 March 2003
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the input file.
!
!    Output, integer ( kind = 4 ) ROW_NUM, the number of rows found.
!
  implicit none

  integer ( kind = 4 ) bad_num
  integer ( kind = 4 ) comment_num
  integer ( kind = 4 ) ierror
  character ( len = * ) input_filename
  integer ( kind = 4 ) input_status
  integer ( kind = 4 ) input_unit
  character ( len = 100 ) line
  integer ( kind = 4 ) record_num
  integer ( kind = 4 ) row_num

  call get_unit ( input_unit )

  open ( unit = input_unit, file = input_filename, status = 'old', &
    iostat = input_status )

  if ( input_status /= 0 ) then
    row_num = -1;
    ierror = 1
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'FILE_ROW_COUNT - Fatal error!'
    write ( *, '(a)' ) '  Could not open the input file: ' // &
      trim ( input_filename )
    stop
  end if

  comment_num = 0
  row_num = 0
  record_num = 0
  bad_num = 0

  do

    read ( input_unit, '(a)', iostat = input_status ) line

    if ( input_status /= 0 ) then
      ierror = record_num
      exit
    end if

    record_num = record_num + 1

    if ( line(1:1) == '#' ) then
      comment_num = comment_num + 1
      cycle
    end if

    if ( len_trim ( line ) == 0 ) then
      comment_num = comment_num + 1
      cycle
    end if

    row_num = row_num + 1

  end do

  close ( unit = input_unit )

  return
end
subroutine get_unit ( iunit )

!*****************************************************************************80
!
!! GET_UNIT returns a free FORTRAN unit number.
!
!  Discussion:
!
!    A "free" FORTRAN unit number is an integer ( kind = 4 ) between 1 and 99 which
!    is not currently associated with an I/O device.  A free FORTRAN unit
!    number is needed in order to open a file with the OPEN command.
!
!    If IUNIT = 0, then no free FORTRAN unit could be found, although
!    all 99 units were checked (except for units 5, 6 and 9, which
!    are commonly reserved for console I/O).
!
!    Otherwise, IUNIT is an integer ( kind = 4 ) between 1 and 99, representing a
!    free FORTRAN unit.  Note that GET_UNIT assumes that units 5 and 6
!    are special, and will never return those values.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    18 September 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Output, integer ( kind = 4 ) IUNIT, the free unit number.
!
  implicit none

  integer ( kind = 4 ) i
  integer ( kind = 4 ) ios
  integer ( kind = 4 ) iunit
  logical lopen

  iunit = 0

  do i = 1, 99

    if ( i /= 5 .and. i /= 6 .and. i /= 9 ) then

      inquire ( unit = i, opened = lopen, iostat = ios )

      if ( ios == 0 ) then
        if ( .not. lopen ) then
          iunit = i
          return
        end if
      end if

    end if

  end do

  return
end
subroutine i4mat_transpose_print_some ( m, n, a, ilo, jlo, ihi, jhi, title )

!*****************************************************************************80
!
!! I4MAT_TRANSPOSE_PRINT_SOME prints some of the transpose of an I4MAT.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    09 February 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) M, N, the number of rows and columns.
!
!    Input, integer ( kind = 4 ) A(M,N), an M by N matrix to be printed.
!
!    Input, integer ( kind = 4 ) ILO, JLO, the first row and column to print.
!
!    Input, integer ( kind = 4 ) IHI, JHI, the last row and column to print.
!
!    Input, character ( len = * ) TITLE, an optional title.
!
  implicit none

  integer ( kind = 4 ), parameter :: incx = 10
  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) a(m,n)
  character ( len = 7 ) ctemp(incx)
  integer ( kind = 4 ) i
  integer ( kind = 4 ) i2
  integer ( kind = 4 ) i2hi
  integer ( kind = 4 ) i2lo
  integer ( kind = 4 ) ihi
  integer ( kind = 4 ) ilo
  integer ( kind = 4 ) inc
  integer ( kind = 4 ) j
  integer ( kind = 4 ) j2hi
  integer ( kind = 4 ) j2lo
  integer ( kind = 4 ) jhi
  integer ( kind = 4 ) jlo
  character ( len = * ) title

  if ( 0 < len_trim ( title ) ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) trim ( title )
  end if

  do i2lo = max ( ilo, 1 ), min ( ihi, m ), incx

    i2hi = i2lo + incx - 1
    i2hi = min ( i2hi, m )
    i2hi = min ( i2hi, ihi )

    inc = i2hi + 1 - i2lo

    write ( *, '(a)' ) ' '

    do i = i2lo, i2hi
      i2 = i + 1 - i2lo
      write ( ctemp(i2), '(i7)') i
    end do

    write ( *, '(''  Row '',10a7)' ) ctemp(1:inc)
    write ( *, '(a)' ) '  Col'
    write ( *, '(a)' ) ' '

    j2lo = max ( jlo, 1 )
    j2hi = min ( jhi, n )

    do j = j2lo, j2hi

      do i2 = 1, inc

        i = i2lo - 1 + i2

        write ( ctemp(i2), '(i7)' ) a(i,j)

      end do

      write ( *, '(i5,1x,10a7)' ) j, ( ctemp(i), i = 1, inc )

    end do

  end do

  write ( *, '(a)' ) ' '

  return
end
subroutine i4row_compare ( m, n, a, i, j, isgn )

!*****************************************************************************80
!
!! I4ROW_COMPARE compares two rows of an I4ROW.
!
!  Example:
!
!    Input:
!
!  M = 3, N = 4, I = 2, J = 3
!
!  A = (
!    1  2  3  4
!    5  6  7  8
!    9 10 11 12 )
!
!    Output:
!
!  ISGN = -1
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    14 November 1999
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) M, N, the number of rows and columns.
!
!    Input, integer ( kind = 4 ) A(M,N), an array of M rows of vectors of length N.
!
!    Input, integer ( kind = 4 ) I, J, the rows to be compared.
!    I and J must be between 1 and M.
!
!    Output, integer ( kind = 4 ) ISGN, the results of the comparison:
!    -1, row I < row J,
!     0, row I = row J,
!    +1, row J < row I.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) a(m,n)
  integer ( kind = 4 ) i
  integer ( kind = 4 ) isgn
  integer ( kind = 4 ) j
  integer ( kind = 4 ) k
!
!  Check that I and J are legal.
!
  if ( i < 1 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_COMPARE - Fatal error!'
    write ( *, '(a)' ) '  Row index I is less than 1.'
    write ( *, '(a,i8)' ) '  I = ', i
    stop
  else if ( m < i ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_COMPARE - Fatal error!'
    write ( *, '(a)' ) '  Row index I is out of bounds.'
    write ( *, '(a,i8)' ) '  I = ', i
    write ( *, '(a,i8)' ) '  Maximum legal value is M = ', m
    stop
  end if

  if ( j < 1 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_COMPARE - Fatal error!'
    write ( *, '(a)' ) '  Row index J is less than 1.'
    write ( *, '(a,i8)' ) '  J = ', j
    stop
  else if ( m < j ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_COMPARE - Fatal error!'
    write ( *, '(a)' ) '  Row index J is out of bounds.'
    write ( *, '(a,i8)' ) '  J = ', j
    write ( *, '(a,i8)' ) '  Maximum legal value is M = ', m
    stop
  end if

  isgn = 0

  if ( i == j ) then
    return
  end if

  k = 1

  do while ( k <= n )

    if ( a(i,k) < a(j,k) ) then
      isgn = -1
      return
    else if ( a(j,k) < a(i,k) ) then
      isgn = +1
      return
    end if

    k = k + 1

  end do

  return
end
subroutine i4row_sort_a ( m, n, a )

!*****************************************************************************80
!
!! I4ROW_SORT_A ascending sorts the rows of an I4ROW.
!
!  Discussion:
!
!    In lexicographic order, the statement "X < Y", applied to two
!    vectors X and Y of length M, means that there is some index I, with
!    1 <= I <= M, with the property that
!
!      X(J) = Y(J) for J < I,
!    and
!      X(I) < Y(I).
!
!    In other words, X is less than Y if, at the first index where they
!    differ, the X value is less than the Y value.
!
!  Example:
!
!    Input:
!
!      M = 5, N = 3
!
!      A =
!        3  2  1
!        2  4  3
!        3  1  8
!        2  4  2
!        1  9  9
!
!    Output:
!
!      A =
!        1  9  9
!        2  4  2
!        2  4  3
!        3  1  8
!        3  2  1
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    25 September 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) M, the number of rows of A.
!
!    Input, integer ( kind = 4 ) N, the number of columns of A.
!
!    Input/output, integer ( kind = 4 ) A(M,N).
!    On input, the array of M rows of N-vectors.
!    On output, the rows of A have been sorted in ascending
!    lexicographic order.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) a(m,n)
  integer ( kind = 4 ) i
  integer ( kind = 4 ) indx
  integer ( kind = 4 ) isgn
  integer ( kind = 4 ) j

  if ( m <= 1 ) then
    return
  end if

  if ( n <= 0 ) then
    return
  end if
!
!  Initialize.
!
  i = 0
  indx = 0
  isgn = 0
  j = 0
!
!  Call the external heap sorter.
!
  do

    call sort_heap_external ( m, indx, i, j, isgn )
!
!  Interchange the I and J objects.
!
    if ( 0 < indx ) then

      call i4row_swap ( m, n, a, i, j )
!
!  Compare the I and J objects.
!
    else if ( indx < 0 ) then

      call i4row_compare ( m, n, a, i, j, isgn )

    else if ( indx == 0 ) then

      exit

    end if

  end do

  return
end
subroutine i4row_swap ( m, n, a, irow1, irow2 )

!*****************************************************************************80
!
!! I4ROW_SWAP swaps two rows of an I4ROW.
!
!  Modified:
!
!    04 April 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) M, N, the number of rows and columns.
!
!    Input/output, integer ( kind = 4 ) A(M,N), an array of data.
!
!    Input, integer ( kind = 4 ) IROW1, IROW2, the two rows to swap.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) a(m,n)
  integer ( kind = 4 ) irow1
  integer ( kind = 4 ) irow2
  integer ( kind = 4 ) row(n)
!
!  Check.
!
  if ( irow1 < 1 .or. m < irow1 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_SWAP - Fatal error!'
    write ( *, '(a)' ) '  IROW1 is out of range.'
    stop
  end if

  if ( irow2 < 1 .or. m < irow2 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4ROW_SWAP - Fatal error!'
    write ( *, '(a)' ) '  IROW2 is out of range.'
    stop
  end if

  if ( irow1 == irow2 ) then
    return
  end if

  row(1:n) = a(irow1,1:n)
  a(irow1,1:n) = a(irow2,1:n)
  a(irow2,1:n) = row(1:n)

  return
end
subroutine itable_data_read ( input_filename, m, n, table )

!*****************************************************************************80
!
!! ITABLE_DATA_READ reads data from an integer ( kind = 4 ) table file.
!
!  Discussion:
!
!    The file may contain more than N points, but this routine
!    will return after reading N points.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    27 January 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the input file.
!
!    Input, integer ( kind = 4 ) M, the spatial dimension.
!
!    Input, integer ( kind = 4 ) N, the number of points.  
!
!    Output, integer ( kind = 4 ) TABLE(M,N), the table data.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) ierror
  character ( len = * ) input_filename
  integer ( kind = 4 ) input_status
  integer ( kind = 4 ) input_unit
  integer ( kind = 4 ) j
  character ( len = 255 ) line
  integer ( kind = 4 ) table(m,n)
  integer ( kind = 4 ) x(m)

  ierror = 0

  call get_unit ( input_unit )

  open ( unit = input_unit, file = input_filename, status = 'old', &
    iostat = input_status )

  if ( input_status /= 0 ) then
    ierror = 1
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'ITABLE_DATA_READ - Fatal error!'
    write ( *, '(a)' ) '  Could not open the input file: ' // &
      trim ( input_filename )
    stop
  end if

  j = 0

  do while ( j < n )

    read ( input_unit, '(a)', iostat = input_status ) line

    if ( input_status /= 0 ) then
      ierror = 2
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'ITABLE_DATA_READ - Fatal error!'
      write ( *, '(a)' ) '  Error while reading lines of data.'
      write ( *, '(a,i8)' ) '  Number of values expected per line M = ', m
      write ( *, '(a,i8)' ) '  Number of data lines read, J =         ', j
      write ( *, '(a,i8)' ) '  Number of data lines needed, N =       ', n
      stop
    end if

    if ( line(1:1) == '#' .or. len_trim ( line ) == 0 ) then
      cycle
    end if

    call s_to_i4vec ( line, m, x, ierror )

    if ( ierror /= 0 ) then
      cycle
    end if

    j = j + 1

    table(1:m,j) = x(1:m)

  end do

  close ( unit = input_unit )

  return
end
subroutine itable_data_write ( output_unit, m, n, table )

!*****************************************************************************80
!
!! ITABLE_DATA_WRITE writes data to an integer ( kind = 4 ) table file.
!
!  Discussion:
!
!    This routine writes a single line of output for each point,
!    containing its spatial coordinates.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    11 March 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) OUTPUT_UNIT, the output unit.
!
!    Input, integer ( kind = 4 ) M, the spatial dimension.
!
!    Input, integer ( kind = 4 ) N, the number of points.
!
!    Input, integer ( kind = 4 ) TABLE(M,N), the table data.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  integer ( kind = 4 ) output_unit
  integer ( kind = 4 ) j
  character ( len = 30 ) string
  integer ( kind = 4 ) table(m,n)
!
!  Create the format string.
!
  write ( string, '(a1,i8,a4)' ) '(', m, 'i10)'
  call s_blank_delete ( string )

  do j = 1, n
    write ( output_unit, string ) table(1:m,j)
  end do

  return
end
subroutine itable_header_read ( input_filename, m, n )

!*****************************************************************************80
!
!! ITABLE_HEADER_READ reads the header from an integer ( kind = 4 ) table file.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    04 June 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) INPUT_FILENAME, the name of the input file.
!
!    Output, integer ( kind = 4 ) M, spatial dimension.
!
!    Output, integer ( kind = 4 ) N, the number of points. 
!
  implicit none

  character ( len = * ) input_filename
  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  call file_column_count ( input_filename, m )

  if ( m <= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'ITABLE_HEADER_READ - Fatal error!'
    write ( *, '(a)' ) '  There was some kind of I/O problem while trying'
    write ( *, '(a)' ) '  to count the number of data columns in'
    write ( *, '(a)' ) '  the file "' // trim ( input_filename ) // '".'
    stop
  end if

  call file_row_count ( input_filename, n )

  if ( n <= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'ITABLE_HEADER_READ - Fatal error!'
    write ( *, '(a)' ) '  There was some kind of I/O problem while trying'
    write ( *, '(a)' ) '  to count the number of data rows in'
    write ( *, '(a)' ) '  the file "' // trim ( input_filename ) // '".'
    stop
  end if

  return
end
subroutine itable_header_write ( output_filename, output_unit, m, n )

!*****************************************************************************80
!
!! ITABLE_HEADER_WRITE writes the header to an integer ( kind = 4 ) table file.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    04 June 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) OUTPUT_FILENAME, the output filename.
!
!    Input, integer ( kind = 4 ) OUTPUT_UNIT, the output unit.
!
!    Input, integer ( kind = 4 ) M, the spatial dimension.
!
!    Input, integer ( kind = 4 ) N, the number of points.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n
  character ( len = * ) output_filename
  integer ( kind = 4 ) output_unit
  character ( len = 40 ) string

  call timestring ( string )

  write ( output_unit, '(a)'       ) '#  ' // trim ( output_filename )
  write ( output_unit, '(a)'       ) '#  created by TRIANGULATION_RCM.F90'
  write ( output_unit, '(a)'       ) '#  at ' // trim ( string )
  write ( output_unit, '(a)'       ) '#'
  write ( output_unit, '(a,i8)'    ) '#  Spatial dimension M = ', m
  write ( output_unit, '(a,i8)'    ) '#  Number of points N =  ', n
  write ( output_unit, '(a)'       ) '#'

  return
end
subroutine itable_write ( output_filename, m, n, table, header )

!*****************************************************************************80
!
!! ITABLE_WRITE writes an integer ( kind = 4 ) table file.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    20 July 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) OUTPUT_FILENAME, the output filename.
!
!    Input, integer ( kind = 4 ) M, the spatial dimension.
!
!    Input, integer ( kind = 4 ) N, the number of points.
!
!    Input, integer ( kind = 4 ) TABLE(M,N), the table data.
!
!    Input, logical HEADER, is TRUE if the header is to be included.
!
  implicit none

  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  logical header
  character ( len = * ) output_filename
  integer ( kind = 4 ) output_status
  integer ( kind = 4 ) output_unit
  integer ( kind = 4 ) table(m,n)

  call get_unit ( output_unit )

  open ( unit = output_unit, file = output_filename, &
    status = 'replace', iostat = output_status )

  if ( output_status /= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'ITABLE_WRITE - Fatal error!'
    write ( *, '(a)' ) '  Could not open the output file "' // &
      trim ( output_filename ) // '".'
    stop
  end if

  if ( header ) then
    call itable_header_write ( output_filename, output_unit, m, n )
  end if

  call itable_data_write ( output_unit, m, n, table )

  close ( unit = output_unit )

  return
end
subroutine r8mat_transpose_print_some ( m, n, a, ilo, jlo, ihi, jhi, title )

!*****************************************************************************80
!
!! R8MAT_TRANSPOSE_PRINT_SOME prints some of an R8MAT, transposed.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    14 June 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) M, N, the number of rows and columns.
!
!    Input, real ( kind = 8 ) A(M,N), an M by N matrix to be printed.
!
!    Input, integer ( kind = 4 ) ILO, JLO, the first row and column to print.
!
!    Input, integer ( kind = 4 ) IHI, JHI, the last row and column to print.
!
!    Input, character ( len = * ) TITLE, an optional title.
!
  implicit none

  integer ( kind = 4 ), parameter :: incx = 5
  integer ( kind = 4 ) m
  integer ( kind = 4 ) n

  real ( kind = 8 ) a(m,n)
  character ( len = 14 ) ctemp(incx)
  integer ( kind = 4 ) i
  integer ( kind = 4 ) i2
  integer ( kind = 4 ) i2hi
  integer ( kind = 4 ) i2lo
  integer ( kind = 4 ) ihi
  integer ( kind = 4 ) ilo
  integer ( kind = 4 ) inc
  integer ( kind = 4 ) j
  integer ( kind = 4 ) j2hi
  integer ( kind = 4 ) j2lo
  integer ( kind = 4 ) jhi
  integer ( kind = 4 ) jlo
  character ( len = * ) title

  if ( 0 < len_trim ( title ) ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) trim ( title )
  end if

  do i2lo = max ( ilo, 1 ), min ( ihi, m ), incx

    i2hi = i2lo + incx - 1
    i2hi = min ( i2hi, m )
    i2hi = min ( i2hi, ihi )

    inc = i2hi + 1 - i2lo

    write ( *, '(a)' ) ' '

    do i = i2lo, i2hi
      i2 = i + 1 - i2lo
      write ( ctemp(i2), '(i7,7x)') i
    end do

    write ( *, '(''  Row   '',5a14)' ) ctemp(1:inc)
    write ( *, '(a)' ) '  Col'
    write ( *, '(a)' ) ' '

    j2lo = max ( jlo, 1 )
    j2hi = min ( jhi, n )

    do j = j2lo, j2hi

      do i2 = 1, inc
        i = i2lo - 1 + i2
        write ( ctemp(i2), '(g14.6)' ) a(i,j)
      end do

      write ( *, '(i5,1x,5a14)' ) j, ( ctemp(i), i = 1, inc )

    end do

  end do

  write ( *, '(a)' ) ' '

  return
end
subroutine s_blank_delete ( s )

!*****************************************************************************80
!
!! S_BLANK_DELETE removes blanks from a string, left justifying the remainder.
!
!  Discussion:
!
!    All TAB characters are also removed.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    26 July 1998
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input/output, character ( len = * ) S, the string to be transformed.
!
  implicit none

  character c
  integer ( kind = 4 ) get
  integer ( kind = 4 ) put
  integer ( kind = 4 ) nchar
  character ( len = * ) s
  character, parameter :: TAB = char ( 9 )

  put = 0
  nchar = len_trim ( s )

  do get = 1, nchar

    c = s(get:get)

    if ( c /= ' ' .and. c /= TAB ) then
      put = put + 1
      s(put:put) = c
    end if

  end do

  s(put+1:nchar) = ' '

  return
end
function s_index_last_c ( s, c )

!*****************************************************************************80
!
!! S_INDEX_LAST_C finds the LAST occurrence of a given character.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    06 December 2003
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, the string to be searched.
!
!    Input, character C, the character to search for.
!
!    Output, integer ( kind = 4 ) S_INDEX_LAST_C, the index in S where C occurs
!    last, or -1 if it does not occur.
!
  implicit none

  character c
  integer ( kind = 4 ) i
  character ( len = * ) s
  integer ( kind = 4 ) s_len
  integer ( kind = 4 ) s_index_last_c

  if ( c == ' ' ) then
    s_len = len ( s )
  else
    s_len = len_trim ( s )
  end if

  do i = s_len, 1, -1

    if ( s(i:i) == c ) then
      s_index_last_c = i
      return
    end if

  end do

  s_index_last_c = -1

  return
end
subroutine s_to_i4 ( s, ival, ierror, length )

!*****************************************************************************80
!
!! S_TO_I4 reads an I4 from a string.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    28 June 2000
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, a string to be examined.
!
!    Output, integer ( kind = 4 ) IVAL, the integer ( kind = 4 ) value read from the string.
!    If the string is blank, then IVAL will be returned 0.
!
!    Output, integer ( kind = 4 ) IERROR, an error flag.
!    0, no error.
!    1, an error occurred.
!
!    Output, integer ( kind = 4 ) LENGTH, the number of characters of S used to make IVAL.
!
  implicit none

  character c
  integer ( kind = 4 ) i
  integer ( kind = 4 ) ierror
  integer ( kind = 4 ) isgn
  integer ( kind = 4 ) istate
  integer ( kind = 4 ) ival
  integer ( kind = 4 ) length
  character ( len = * ) s

  ierror = 0
  istate = 0
  isgn = 1
  ival = 0

  do i = 1, len_trim ( s )

    c = s(i:i)
!
!  Haven't read anything.
!
    if ( istate == 0 ) then

      if ( c == ' ' ) then

      else if ( c == '-' ) then
        istate = 1
        isgn = -1
      else if ( c == '+' ) then
        istate = 1
        isgn = + 1
      else if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        istate = 2
        ival = ichar ( c ) - ichar ( '0' )
      else
        ierror = 1
        return
      end if
!
!  Have read the sign, expecting digits.
!
    else if ( istate == 1 ) then

      if ( c == ' ' ) then

      else if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        istate = 2
        ival = ichar ( c ) - ichar ( '0' )
      else
        ierror = 1
        return
      end if
!
!  Have read at least one digit, expecting more.
!
    else if ( istate == 2 ) then

      if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        ival = 10 * ival + ichar ( c ) - ichar ( '0' )
      else
        ival = isgn * ival
        length = i - 1
        return
      end if

    end if

  end do
!
!  If we read all the characters in the string, see if we're OK.
!
  if ( istate == 2 ) then
    ival = isgn * ival
    length = len_trim ( s )
  else
    ierror = 1
    length = 0
  end if

  return
end
subroutine s_to_i4vec ( s, n, ivec, ierror )

!*****************************************************************************80
!
!! S_TO_I4VEC reads an I4VEC from a string.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    08 October 2003
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, the string to be read.
!
!    Input, integer ( kind = 4 ) N, the number of values expected.
!
!    Output, integer ( kind = 4 ) IVEC(N), the values read from the string.
!
!    Output, integer ( kind = 4 ) IERROR, error flag.
!    0, no errors occurred.
!    -K, could not read data for entries -K through N.
!
  implicit none

  integer ( kind = 4 ) n

  integer ( kind = 4 ) i
  integer ( kind = 4 ) ierror
  integer ( kind = 4 ) ilo
  integer ( kind = 4 ) ivec(n)
  integer ( kind = 4 ) length
  character ( len = * ) s

  i = 0
  ierror = 0
  ilo = 1

  do while ( i < n )

    i = i + 1

    call s_to_i4 ( s(ilo:), ivec(i), ierror, length )

    if ( ierror /= 0 ) then
      ierror = -i
      exit
    end if

    ilo = ilo + length

  end do

  return
end
subroutine s_to_r8 ( s, dval, ierror, length )

!*****************************************************************************80
!
!! S_TO_R8 reads an R8 from a string.
!
!  Discussion:
!
!    The routine will read as many characters as possible until it reaches
!    the end of the string, or encounters a character which cannot be
!    part of the number.
!
!    Legal input is:
!
!       1 blanks,
!       2 '+' or '-' sign,
!       2.5 blanks
!       3 integer ( kind = 4 ) part,
!       4 decimal point,
!       5 fraction part,
!       6 'E' or 'e' or 'D' or 'd', exponent marker,
!       7 exponent sign,
!       8 exponent integer ( kind = 4 ) part,
!       9 exponent decimal point,
!      10 exponent fraction part,
!      11 blanks,
!      12 final comma or semicolon,
!
!    with most quantities optional.
!
!  Example:
!
!    S                 DVAL
!
!    '1'               1.0
!    '     1   '       1.0
!    '1A'              1.0
!    '12,34,56'        12.0
!    '  34 7'          34.0
!    '-1E2ABCD'        -100.0
!    '-1X2ABCD'        -1.0
!    ' 2E-1'           0.2
!    '23.45'           23.45
!    '-4.2E+2'         -420.0
!    '17d2'            1700.0
!    '-14e-2'         -0.14
!    'e2'              100.0
!    '-12.73e-9.23'   -12.73 * 10.0**(-9.23)
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    07 September 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, the string containing the
!    data to be read.  Reading will begin at position 1 and
!    terminate at the end of the string, or when no more
!    characters can be read to form a legal real.  Blanks,
!    commas, or other nonnumeric data will, in particular,
!    cause the conversion to halt.
!
!    Output, real ( kind = 8 ) DVAL, the value read from the string.
!
!    Output, integer ( kind = 4 ) IERROR, error flag.
!    0, no errors occurred.
!    1, 2, 6 or 7, the input number was garbled.  The
!    value of IERROR is the last type of input successfully
!    read.  For instance, 1 means initial blanks, 2 means
!    a plus or minus sign, and so on.
!
!    Output, integer ( kind = 4 ) LENGTH, the number of characters read
!    to form the number, including any terminating
!    characters such as a trailing comma or blanks.
!
  implicit none

  logical ch_eqi
  character c
  real ( kind = 8 ) dval
  integer ( kind = 4 ) ierror
  integer ( kind = 4 ) ihave
  integer ( kind = 4 ) isgn
  integer ( kind = 4 ) iterm
  integer ( kind = 4 ) jbot
  integer ( kind = 4 ) jsgn
  integer ( kind = 4 ) jtop
  integer ( kind = 4 ) length
  integer ( kind = 4 ) nchar
  integer ( kind = 4 ) ndig
  real ( kind = 8 ) rbot
  real ( kind = 8 ) rexp
  real ( kind = 8 ) rtop
  character ( len = * ) s

  nchar = len_trim ( s )

  ierror = 0
  dval = 0.0D+00
  length = -1
  isgn = 1
  rtop = 0
  rbot = 1
  jsgn = 1
  jtop = 0
  jbot = 1
  ihave = 1
  iterm = 0

  do

    length = length + 1

    if ( nchar < length+1 ) then
      exit
    end if

    c = s(length+1:length+1)
!
!  Blank character.
!
    if ( c == ' ' ) then

      if ( ihave == 2 ) then

      else if ( ihave == 6 .or. ihave == 7 ) then
        iterm = 1
      else if ( 1 < ihave ) then
        ihave = 11
      end if
!
!  Comma.
!
    else if ( c == ',' .or. c == ';' ) then

      if ( ihave /= 1 ) then
        iterm = 1
        ihave = 12
        length = length + 1
      end if
!
!  Minus sign.
!
    else if ( c == '-' ) then

      if ( ihave == 1 ) then
        ihave = 2
        isgn = -1
      else if ( ihave == 6 ) then
        ihave = 7
        jsgn = -1
      else
        iterm = 1
      end if
!
!  Plus sign.
!
    else if ( c == '+' ) then

      if ( ihave == 1 ) then
        ihave = 2
      else if ( ihave == 6 ) then
        ihave = 7
      else
        iterm = 1
      end if
!
!  Decimal point.
!
    else if ( c == '.' ) then

      if ( ihave < 4 ) then
        ihave = 4
      else if ( 6 <= ihave .and. ihave <= 8 ) then
        ihave = 9
      else
        iterm = 1
      end if
!
!  Scientific notation exponent marker.
!
    else if ( ch_eqi ( c, 'E' ) .or. ch_eqi ( c, 'D' ) ) then

      if ( ihave < 6 ) then
        ihave = 6
      else
        iterm = 1
      end if
!
!  Digit.
!
    else if (  ihave < 11 .and. lle ( '0', c ) .and. lle ( c, '9' ) ) then

      if ( ihave <= 2 ) then
        ihave = 3
      else if ( ihave == 4 ) then
        ihave = 5
      else if ( ihave == 6 .or. ihave == 7 ) then
        ihave = 8
      else if ( ihave == 9 ) then
        ihave = 10
      end if

      call ch_to_digit ( c, ndig )

      if ( ihave == 3 ) then
        rtop = 10.0D+00 * rtop + real ( ndig, kind = 8 )
      else if ( ihave == 5 ) then
        rtop = 10.0D+00 * rtop + real ( ndig, kind = 8 )
        rbot = 10.0D+00 * rbot
      else if ( ihave == 8 ) then
        jtop = 10 * jtop + ndig
      else if ( ihave == 10 ) then
        jtop = 10 * jtop + ndig
        jbot = 10 * jbot
      end if
!
!  Anything else is regarded as a terminator.
!
    else
      iterm = 1
    end if
!
!  If we haven't seen a terminator, and we haven't examined the
!  entire string, go get the next character.
!
    if ( iterm == 1 ) then
      exit
    end if

  end do
!
!  If we haven't seen a terminator, and we have examined the
!  entire string, then we're done, and LENGTH is equal to NCHAR.
!
  if ( iterm /= 1 .and. length+1 == nchar ) then
    length = nchar
  end if
!
!  Number seems to have terminated.  Have we got a legal number?
!  Not if we terminated in states 1, 2, 6 or 7!
!
  if ( ihave == 1 .or. ihave == 2 .or. ihave == 6 .or. ihave == 7 ) then
    ierror = ihave
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'S_TO_R8 - Serious error!'
    write ( *, '(a)' ) '  Illegal or nonnumeric input:'
    write ( *, '(a)' ) '    ' // trim ( s )
    return
  end if
!
!  Number seems OK.  Form it.
!
  if ( jtop == 0 ) then
    rexp = 1.0D+00
  else
    if ( jbot == 1 ) then
      rexp = 10.0D+00 ** ( jsgn * jtop )
    else
      rexp = 10.0D+00 ** ( real ( jsgn * jtop, kind = 8 ) &
        / real ( jbot, kind = 8 ) )
    end if
  end if

  dval = real ( isgn, kind = 8 ) * rexp * rtop / rbot

  return
end
subroutine s_to_r8vec ( s, n, rvec, ierror )

!*****************************************************************************80
!
!! S_TO_R8VEC reads an R8VEC from a string.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    07 September 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, the string to be read.
!
!    Input, integer ( kind = 4 ) N, the number of values expected.
!
!    Output, real ( kind = 8 ) RVEC(N), the values read from the string.
!
!    Output, integer ( kind = 4 ) IERROR, error flag.
!    0, no errors occurred.
!    -K, could not read data for entries -K through N.
!
  implicit none

  integer ( kind = 4 ) n

  integer ( kind = 4 ) i
  integer ( kind = 4 ) ierror
  integer ( kind = 4 ) ilo
  integer ( kind = 4 ) lchar
  real ( kind = 8 ) rvec(n)
  character ( len = * ) s

  i = 0
  ierror = 0
  ilo = 1

  do while ( i < n )

    i = i + 1

    call s_to_r8 ( s(ilo:), rvec(i), ierror, lchar )

    if ( ierror /= 0 ) then
      ierror = -i
      exit
    end if

    ilo = ilo + lchar

  end do

  return
end
subroutine s_word_count ( s, nword )

!*****************************************************************************80
!
!! S_WORD_COUNT counts the number of "words" in a string.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    14 April 1999
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, the string to be examined.
!
!    Output, integer ( kind = 4 ) NWORD, the number of "words" in the string.
!    Words are presumed to be separated by one or more blanks.
!
  implicit none

  logical blank
  integer ( kind = 4 ) i
  integer ( kind = 4 ) lens
  integer ( kind = 4 ) nword
  character ( len = * ) s

  nword = 0
  lens = len ( s )

  if ( lens <= 0 ) then
    return
  end if

  blank = .true.

  do i = 1, lens

    if ( s(i:i) == ' ' ) then
      blank = .true.
    else if ( blank ) then
      nword = nword + 1
      blank = .false.
    end if

  end do

  return
end
subroutine sort_heap_external ( n, indx, i, j, isgn )

!*****************************************************************************80
!
!! SORT_HEAP_EXTERNAL externally sorts a list of items into ascending order.
!
!  Discussion:
!
!    The actual list of data is not passed to the routine.  Hence this
!    routine may be used to sort integer ( kind = 4 )s, reals, numbers, names,
!    dates, shoe sizes, and so on.  After each call, the routine asks
!    the user to compare or interchange two items, until a special
!    return value signals that the sorting is completed.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    05 February 2004
!
!  Author:
!
!    FORTRAN77 original version by Albert Nijenhuis, Herbert Wilf.
!    FORTRAN90 version by John Burkardt
!
!  Reference:
!
!    Albert Nijenhuis and Herbert Wilf,
!    Combinatorial Algorithms,
!    Academic Press, 1978, second edition,
!    ISBN 0-12-519260-6.
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) N, the number of items to be sorted.
!
!    Input/output, integer ( kind = 4 ) INDX, the main communication signal.
!
!    The user must set INDX to 0 before the first call.
!    Thereafter, the user should not change the value of INDX until
!    the sorting is done.
!
!    On return, if INDX is
!
!      greater than 0,
!      * interchange items I and J;
!      * call again.
!
!      less than 0,
!      * compare items I and J;
!      * set ISGN = -1 if I < J, ISGN = +1 if J < I;
!      * call again.
!
!      equal to 0, the sorting is done.
!
!    Output, integer ( kind = 4 ) I, J, the indices of two items.
!    On return with INDX positive, elements I and J should be interchanged.
!    On return with INDX negative, elements I and J should be compared, and
!    the result reported in ISGN on the next call.
!
!    Input, integer ( kind = 4 ) ISGN, results of comparison of elements I and J.
!    (Used only when the previous call returned INDX less than 0).
!    ISGN <= 0 means I is less than or equal to J;
!    0 <= ISGN means I is greater than or equal to J.
!
  implicit none

  integer ( kind = 4 ) i
  integer ( kind = 4 ), save :: i_save = 0
  integer ( kind = 4 ) indx
  integer ( kind = 4 ) isgn
  integer ( kind = 4 ) j
  integer ( kind = 4 ), save :: j_save = 0
  integer ( kind = 4 ), save :: k = 0
  integer ( kind = 4 ), save :: k1 = 0
  integer ( kind = 4 ) n
  integer ( kind = 4 ), save :: n1 = 0
!
!  INDX = 0: This is the first call.
!
  if ( indx == 0 ) then

    i_save = 0
    j_save = 0
    k = n / 2
    k1 = k
    n1 = n
!
!  INDX < 0: The user is returning the results of a comparison.
!
  else if ( indx < 0 ) then

    if ( indx == -2 ) then

      if ( isgn < 0 ) then
        i_save = i_save + 1
      end if

      j_save = k1
      k1 = i_save
      indx = -1
      i = i_save
      j = j_save
      return

    end if

    if ( 0 < isgn ) then
      indx = 2
      i = i_save
      j = j_save
      return
    end if

    if ( k <= 1 ) then

      if ( n1 == 1 ) then
        i_save = 0
        j_save = 0
        indx = 0
      else
        i_save = n1
        n1 = n1 - 1
        j_save = 1
        indx = 1
      end if

      i = i_save
      j = j_save
      return

    end if

    k = k - 1
    k1 = k
!
!  0 < INDX, the user was asked to make an interchange.
!
  else if ( indx == 1 ) then

    k1 = k

  end if

  do

    i_save = 2 * k1

    if ( i_save == n1 ) then
      j_save = k1
      k1 = i_save
      indx = -1
      i = i_save
      j = j_save
      return
    else if ( i_save <= n1 ) then
      j_save = i_save + 1
      indx = -2
      i = i_save
      j = j_save
      return
    end if

    if ( k <= 1 ) then
      exit
    end if

    k = k - 1
    k1 = k

  end do

  if ( n1 == 1 ) then
    i_save = 0
    j_save = 0
    indx = 0
    i = i_save
    j = j_save
  else
    i_save = n1
    n1 = n1 - 1
    j_save = 1
    indx = 1
    i = i_save
    j = j_save
  end if

  return
end
subroutine timestamp ( )

!*****************************************************************************80
!
!! TIMESTAMP prints the current YMDHMS date as a time stamp.
!
!  Example:
!
!    May 31 2001   9:45:54.872 AM
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    31 May 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    None
!
  implicit none

  character ( len = 8 ) ampm
  integer ( kind = 4 ) d
  character ( len = 8 ) date
  integer ( kind = 4 ) h
  integer ( kind = 4 ) m
  integer ( kind = 4 ) mm
  character ( len = 9 ), parameter, dimension(12) :: month = (/ &
    'January  ', 'February ', 'March    ', 'April    ', &
    'May      ', 'June     ', 'July     ', 'August   ', &
    'September', 'October  ', 'November ', 'December ' /)
  integer ( kind = 4 ) n
  integer ( kind = 4 ) s
  character ( len = 10 )  time
  integer ( kind = 4 ) values(8)
  integer ( kind = 4 ) y
  character ( len = 5 ) zone

  call date_and_time ( date, time, zone, values )

  y = values(1)
  m = values(2)
  d = values(3)
  h = values(5)
  n = values(6)
  s = values(7)
  mm = values(8)

  if ( h < 12 ) then
    ampm = 'AM'
  else if ( h == 12 ) then
    if ( n == 0 .and. s == 0 ) then
      ampm = 'Noon'
    else
      ampm = 'PM'
    end if
  else
    h = h - 12
    if ( h < 12 ) then
      ampm = 'PM'
    else if ( h == 12 ) then
      if ( n == 0 .and. s == 0 ) then
        ampm = 'Midnight'
      else
        ampm = 'AM'
      end if
    end if
  end if

  write ( *, '(a,1x,i2,1x,i4,2x,i2,a1,i2.2,a1,i2.2,a1,i3.3,1x,a)' ) &
    trim ( month(m) ), d, y, h, ':', n, ':', s, '.', mm, trim ( ampm )

  return
end
subroutine timestring ( string )

!*****************************************************************************80
!
!! TIMESTRING writes the current YMDHMS date into a string.
!
!  Example:
!
!    STRING = 'May 31 2001   9:45:54.872 AM'
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    15 March 2003
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Output, character ( len = * ) STRING, contains the date information.
!    A character length of 40 should always be sufficient.
!
  implicit none

  character ( len = 8 ) ampm
  integer ( kind = 4 ) d
  character ( len = 8 ) date
  integer ( kind = 4 ) h
  integer ( kind = 4 ) m
  integer ( kind = 4 ) mm
  character ( len = 9 ), parameter, dimension(12) :: month = (/ &
    'January  ', 'February ', 'March    ', 'April    ', &
    'May      ', 'June     ', 'July     ', 'August   ', &
    'September', 'October  ', 'November ', 'December ' /)
  integer ( kind = 4 ) n
  integer ( kind = 4 ) s
  character ( len = * ) string
  character ( len = 10 )  time
  integer ( kind = 4 ) values(8)
  integer ( kind = 4 ) y
  character ( len = 5 ) zone

  call date_and_time ( date, time, zone, values )

  y = values(1)
  m = values(2)
  d = values(3)
  h = values(5)
  n = values(6)
  s = values(7)
  mm = values(8)

  if ( h < 12 ) then
    ampm = 'AM'
  else if ( h == 12 ) then
    if ( n == 0 .and. s == 0 ) then
      ampm = 'Noon'
    else
      ampm = 'PM'
    end if
  else
    h = h - 12
    if ( h < 12 ) then
      ampm = 'PM'
    else if ( h == 12 ) then
      if ( n == 0 .and. s == 0 ) then
        ampm = 'Midnight'
      else
        ampm = 'AM'
      end if
    end if
  end if

  write ( string, '(a,1x,i2,1x,i4,2x,i2,a1,i2.2,a1,i2.2,a1,i3.3,1x,a)' ) &
    trim ( month(m) ), d, y, h, ':', n, ':', s, '.', mm, trim ( ampm )

  return
end
subroutine triangulation_order3_neighbor_triangles ( triangle_num, tri_vert, &
  tri_nabe )

!*****************************************************************************80
!
!! TRIANGULATION_ORDER3_NEIGHBOR_TRIANGLES determines triangle neighbors.
!
!  Discussion:
!
!    A triangulation of a set of nodes can be completely described by
!    the coordinates of the nodes, and the list of nodes that make up
!    each triangle.  However, in some cases, it is necessary to know
!    triangle adjacency information, that is, which triangle, if any,
!    is adjacent to a given triangle on a particular side.
!
!    This routine creates a data structure recording this information.
!
!    The primary amount of work occurs in sorting a list of 3 * TRIANGLE_NUM
!    data items.
!
!  Example:
!
!    The input information from TRI_VERT:
!
!    Triangle   Nodes
!    --------   ---------------
!     1         3      4      1
!     2         3      1      2
!     3         3      2      8
!     4         2      1      5
!     5         8      2     13
!     6         8     13      9
!     7         3      8      9
!     8        13      2      5
!     9         9     13      7
!    10         7     13      5
!    11         6      7      5
!    12         9      7      6
!    13        10      9      6
!    14         6      5     12
!    15        11      6     12
!    16        10      6     11
!
!    The output information in TRI_NABE:
!
!    Triangle  Neighboring Triangles
!    --------  ---------------------
!
!     1        -1     -1      2
!     2         1      4      3
!     3         2      5      7
!     4         2     -1      8
!     5         3      8      6
!     6         5      9      7
!     7         3      6     -1
!     8         5      4     10
!     9         6     10     12
!    10         9      8     11
!    11        12     10     14
!    12         9     11     13
!    13        -1     12     16
!    14        11     -1     15
!    15        16     14     -1
!    16        13     15     -1
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    17 July 2001
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) TRIANGLE_NUM, the number of triangles.
!
!    Input, integer ( kind = 4 ) TRI_VERT(3,TRIANGLE_NUM), the nodes that make up each triangle.
!
!    Output, integer ( kind = 4 ) TRI_NABE(3,TRIANGLE_NUM), the three triangles that are direct
!    neighbors of a given triangle.  TRI_NABE(1,I) is the index of the triangle
!    which touches side 1, defined by nodes 2 and 3, and so on.  TRI_NABE(1,I)
!    is negative if there is no neighbor on that side.  In this case, that
!    side of the triangle lies on the boundary of the triangulation.
!
  implicit none

  integer ( kind = 4 ) triangle_num

  integer ( kind = 4 ) i
  integer ( kind = 4 ) irow
  integer ( kind = 4 ) j
  integer ( kind = 4 ) k
  integer ( kind = 4 ) row(3*triangle_num,4)
  integer ( kind = 4 ) side1
  integer ( kind = 4 ) side2
  integer ( kind = 4 ) tri_nabe(3,triangle_num)
  integer ( kind = 4 ) tri
  integer ( kind = 4 ) tri_vert(3,triangle_num)
  integer ( kind = 4 ) tri1
  integer ( kind = 4 ) tri2
!
!  Step 1.
!  From the list of nodes for triangle T, of the form: (I,J,K)
!  construct the three neighbor relations:
!
!    (I,J,1,T) or (J,I,1,T),
!    (J,K,2,T) or (K,J,2,T),
!    (K,I,3,T) or (I,K,3,T)
!
!  where we choose (I,J,1,T) if I < J, or else (J,I,1,T)
!
  do tri = 1, triangle_num

    i = tri_vert(1,tri)
    j = tri_vert(2,tri)
    k = tri_vert(3,tri)

    if ( i < j ) then
      row(3*(tri-1)+1,1:4) = (/ i, j, 1, tri /)
    else
      row(3*(tri-1)+1,1:4) = (/ j, i, 1, tri /)
    end if

    if ( j < k ) then
      row(3*(tri-1)+2,1:4) = (/ j, k, 2, tri /)
    else
      row(3*(tri-1)+2,1:4) = (/ k, j, 2, tri /)
    end if

    if ( k < i ) then
      row(3*(tri-1)+3,1:4) = (/ k, i, 3, tri /)
    else
      row(3*(tri-1)+3,1:4) = (/ i, k, 3, tri /)
    end if

  end do
!
!  Step 2. Perform an ascending dictionary sort on the neighbor relations.
!  We only intend to sort on columns 1 and 2; the routine we call here
!  sorts on columns 1 through 4 but that won't hurt us.
!
!  What we need is to find cases where two triangles share an edge.
!  Say they share an edge defined by the nodes I and J.  Then there are
!  two rows of ROW that start out ( I, J, ?, ? ).  By sorting ROW,
!  we make sure that these two rows occur consecutively.  That will
!  make it easy to notice that the triangles are neighbors.
!
  call i4row_sort_a ( 3*triangle_num, 4, row )
!
!  Step 3. Neighboring triangles show up as consecutive rows with
!  identical first two entries.  Whenever you spot this happening,
!  make the appropriate entries in TRI_NABE.
!
  tri_nabe(1:3,1:triangle_num) = -1

  irow = 1

  do

    if ( 3 * triangle_num <= irow ) then
      exit
    end if

    if ( row(irow,1) /= row(irow+1,1) .or. row(irow,2) /= row(irow+1,2) ) then
      irow = irow + 1
      cycle
    end if

    side1 = row(irow,3)
    tri1 = row(irow,4)
    side2 = row(irow+1,3)
    tri2 = row(irow+1,4)

    tri_nabe(side1,tri1) = tri2
    tri_nabe(side2,tri2) = tri1

    irow = irow + 2

  end do

  return
end
subroutine triangulation_order6_neighbor_triangles ( triangle_num, tri_vert, &
  tri_nabe )

!*****************************************************************************80
!
!! TRIANGULATION_ORDER6_NEIGHBOR_TRIANGLES determines triangle neighbors.
!
!  Discussion:
!
!    A triangulation of a set of nodes can be completely described by
!    the coordinates of the nodes, and the list of nodes that make up
!    each triangle.  However, in some cases, it is necessary to know
!    triangle adjacency information, that is, which triangle, if any,
!    is adjacent to a given triangle on a particular side.
!
!    This routine creates a data structure recording this information.
!
!    The primary amount of work occurs in sorting a list of 3 * TRIANGLE_NUM
!    data items.
!
!  Licensing:
!
!    This code is distributed under the GNU LGPL license. 
!
!  Modified:
!
!    12 March 2005
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, integer ( kind = 4 ) TRIANGLE_NUM, the number of triangles.
!
!    Input, integer ( kind = 4 ) TRI_VERT(6,TRIANGLE_NUM), the nodes that make up each triangle.
!
!    Output, integer ( kind = 4 ) TRI_NABE(3,TRIANGLE_NUM), the three triangles that are direct
!    neighbors of a given triangle.  TRI_NABE(1,I) is the index of the triangle
!    which touches side 1, defined by nodes 2 and 3, and so on.  TRI_NABE(1,I)
!    is negative if there is no neighbor on that side.  In this case, that
!    side of the triangle lies on the boundary of the triangulation.
!
  implicit none

  integer ( kind = 4 ) triangle_num

  integer ( kind = 4 ) i
  integer ( kind = 4 ) irow
  integer ( kind = 4 ) j
  integer ( kind = 4 ) k
  integer ( kind = 4 ) row(3*triangle_num,4)
  integer ( kind = 4 ) side1
  integer ( kind = 4 ) side2
  integer ( kind = 4 ) tri_nabe(3,triangle_num)
  integer ( kind = 4 ) tri
  integer ( kind = 4 ) tri_vert(6,triangle_num)
  integer ( kind = 4 ) tri1
  integer ( kind = 4 ) tri2
!
!  Step 1.
!  From the list of vertices for triangle T, of the form: (I,J,K)
!  construct the three neighbor relations:
!
!    (I,J,1,T) or (J,I,1,T),
!    (J,K,2,T) or (K,J,2,T),
!    (K,I,3,T) or (I,K,3,T)
!
!  where we choose (I,J,1,T) if I < J, or else (J,I,1,T)
!
  do tri = 1, triangle_num

    i = tri_vert(1,tri)
    j = tri_vert(2,tri)
    k = tri_vert(3,tri)

    if ( i < j ) then
      row(3*(tri-1)+1,1:4) = (/ i, j, 1, tri /)
    else
      row(3*(tri-1)+1,1:4) = (/ j, i, 1, tri /)
    end if

    if ( j < k ) then
      row(3*(tri-1)+2,1:4) = (/ j, k, 2, tri /)
    else
      row(3*(tri-1)+2,1:4) = (/ k, j, 2, tri /)
    end if

    if ( k < i ) then
      row(3*(tri-1)+3,1:4) = (/ k, i, 3, tri /)
    else
      row(3*(tri-1)+3,1:4) = (/ i, k, 3, tri /)
    end if

  end do
!
!  Step 2. Perform an ascending dictionary sort on the neighbor relations.
!  We only intend to sort on columns 1 and 2; the routine we call here
!  sorts on columns 1 through 4 but that won't hurt us.
!
!  What we need is to find cases where two triangles share an edge.
!  Say they share an edge defined by the nodes I and J.  Then there are
!  two rows of ROW that start out ( I, J, ?, ? ).  By sorting ROW,
!  we make sure that these two rows occur consecutively.  That will
!  make it easy to notice that the triangles are neighbors.
!
  call i4row_sort_a ( 3*triangle_num, 4, row )
!
!  Step 3. Neighboring triangles show up as consecutive rows with
!  identical first two entries.  Whenever you spot this happening,
!  make the appropriate entries in TRI_NABE.
!
  tri_nabe(1:3,1:triangle_num) = -1

  irow = 1

  do

    if ( 3 * triangle_num <= irow ) then
      exit
    end if

    if ( row(irow,1) /= row(irow+1,1) .or. row(irow,2) /= row(irow+1,2) ) then
      irow = irow + 1
      cycle
    end if

    side1 = row(irow,3)
    tri1 = row(irow,4)
    side2 = row(irow+1,3)
    tri2 = row(irow+1,4)

    tri_nabe(side1,tri1) = tri2
    tri_nabe(side2,tri2) = tri1

    irow = irow + 2

  end do

  return
end