program main

!*****************************************************************************80
!
!! MAIN is the main program for NIEDERREITER2_DATASET.
!
!  Discussion:
!
!    NIEDERREITER2_DATASET generates a Niederreiter2 dataset and writes it out.
!
!    These program assumes that your computer's word length
!    is 31 bits, excluding sign.  If this is not the case,
!    modify the parameter NBITS throughout accordingly.
!
!  Modified:
!
!    14 April 2003
!
!  Author:
!
!    John Burkardt
!
!  Reference:
!
!    Paul Bratley, Bennett Fox, Harald Niederreiter,
!    Algorithm 738: 
!    Programs to Generate Niederreiter's Low-Discrepancy Sequences,
!    ACM Transactions on Mathematical Software,
!    Volume 20, Number 4, pages 494-495, 1994.
!
!  Local Parameters:
!
!    Local, integer DIM_MAX, the maximum dimension that will be used.  
!
!    Local, integer POWER, is used in a possible warm-up formula.
!
  implicit none

  integer, parameter :: dim_max = 20

  integer, parameter :: base = 2
  integer dim_num
  character ( len = 80 ) :: file_out_name
  integer ios
  integer n
  integer, parameter :: power = 12
  real, allocatable, dimension ( :, : ) :: r
  integer :: seed = 123456789
  integer skip

  call timestamp ( )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'NIEDERREITER2_DATASET'
  write ( *, '(a)' ) '  FORTRAN90 version'
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Show a Niederreiter sequence for a given'
  write ( *, '(a)' ) '  spatial dimension.'
  write ( *, '(a)' ) ' '

  do

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Enter the spatial dimension'
    write ( *, '(a,i6)' ) '  between 1 and ', dim_max
    write ( *, '(a)' ) '  (A 0 or negative value terminates execution.)'

    read ( *, *, iostat = ios ) dim_num

    if ( ios /= 0 ) then
      exit
    end if

    if ( dim_num <= 0 ) then
      exit
    end if

    if ( dim_max < dim_num ) then
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'NIEDERREITER2_DATASET - Error!'
      write ( *, '(a,i6)' ) '  The dimension may not exceed ', dim_max
      cycle
    end if
!
!  The sequence length is the number of quasi-random points used to 
!  estimate the integral, excluding warm-up.
!
!  Some users may wish to rewrite the driver to test a [heuristic] 
!  "convergence" criterion, stopping the generation of points
!  when it is passed or when a specified number of points have been 
!  generated, whichever occurs first.
!
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Choose the sequence length:'
!
!  Except when comparing results with other bases, we suggest taking 
!  N to be a power of 2.
!
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  If you do not have a preference, we'
    write ( *, '(a)' ) '  suggest using a large power of two, such as:'
    write ( *, '(a)' ) ' '
    write ( *, '(a,i12)' ) '  2**10 = ', 2**10
    write ( *, '(a,i12)' ) '  2**15 = ', 2**15
    write ( *, '(a,i12)' ) '  2**20 = ', 2**20
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Enter the sequence length:'

    read ( *, *, iostat = ios ) n

    if ( ios /= 0 ) then
      exit
    end if

    if ( n <= 0 ) then
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'NIEDERREITER2_DATASET - Error!'
      write ( *, '(a)' ) '  The sequence length must be strictly positive.'
      cycle
    end if

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Choose the number of values to skip:'
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  There is reason to believe that BASE**E, '
    write ( *, '(a)' ) '  where E is defined for example in '
    write ( *, '(a)' ) '  Bratley, Fox, and Niederreiter [1991], '
    write ( *, '(a)' ) '  would be a good choice.  Our formula has '
    write ( *, '(a)' ) '  has the form:'
    write ( *, '(a)' ) '    SKIP = 2 ** POWER,'
    write ( *, '(a)' ) '  where POWER is chosen so that SKIP comes nowhere '
    write ( *, '(a)' ) '  near the largest possible machine-representable'
    write ( *, '(a)' ) '  integer.  It does not hurt to choose '
    write ( *, '(a)' ) '  POWER larger than E, because skipping is '
    write ( *, '(a)' ) '  done implicitly in O(1) time. '
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  The maximum value of E for a fixed dimension '
    write ( *, '(a)' ) '  S grows like log S.  We allow some "fat" for '
    write ( *, '(a)' ) '  the implicit constant. '
    write ( *, '(a)' ) ' '
    write ( *, '(a,i12)' ) '  Numerically, 2**POWER = ', 2 ** power
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Enter SKIP (not necessarily the value above)'

    read ( *, *, iostat = ios ) skip

    if ( ios /= 0 ) then
      exit
    end if

    if ( skip < 0 ) then
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'NIEDERREITER2_DATASET - Error!'
      write ( *, '(a)' ) '  The skip value must be nonnegative.'
      cycle
    end if

    allocate ( r(1:dim_num,1:n) )

    call niederreiter2_generate ( dim_num, n, seed, r )

    write ( file_out_name, '(a,i2.2,a,i5.5,a)' ) &
      'niederreiter2_', dim_num, '_', n, '.txt'

    call niederreiter_write ( dim_num, n, base, skip, r, file_out_name )

    deallocate ( r )

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'NIEDERREITER2_DATASET:'
    write ( *, '(a)' ) '  Output file name is ' // trim ( file_out_name )

  end do

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'NIEDERREITER2_DATASET:'
  write ( *, '(a)' ) '  Normal end of execution.'

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

  stop
end