function node_r = residual_adjust_dirichlet ( node_num, node_xy, ...
  node_p_variable, node_u_variable, node_v_variable, node_p_condition, ...
  node_u_condition, node_v_condition, variable_num, node_c, node_r )

%% RESIDUAL_ADJUST_DIRICHLET adjusts the residual for Dirichlet conditions.
%
%  Modified:
%
%    08 September 2006
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, integer NODE_NUM, the number of nodes.
%
%    Input, real NODE_XY(2,NODE_NUM), the coordinates of nodes.
%
%    Input, integer NODE_P_VARIABLE(NODE_NUM),
%    is the index of the pressure variable associated with the node,
%    or -1 if there is no associated pressure variable.
%
%    Input, integer NODE_U_VARIABLE(NODE_NUM),
%    is the index of the horizontal velocity variable associated with the node.
%
%    Input, integer NODE_V_VARIABLE(NODE_NUM),
%    is the index of the vertical velocity variable associated with the node.
%
%    Input, integer NODE_P_CONDITION(NODE_NUM),
%    indicates the condition used to determine pressure at a node.
%    0, there is no condition at this node.
%    1, a finite element equation is used;
%    2, a Dirichlet condition is used.
%    3, a Neumann condition is used.
%
%    Input, integer NODE_U_CONDITION(NODE_NUM),
%    indicates the condition used to determine horizontal velocity at a node.
%    0, there is no condition at this node.
%    1, a finite element equation is used;
%    2, a Dirichlet condition is used.
%    3, a Neumann condition is used.
%
%    Input, integer NODE_V_CONDITION(NODE_NUM),
%    indicates the condition used to determine vertical velocity at a node.
%    0, there is no condition at this node.
%    1, a finite element equation is used;
%    2, a Dirichlet condition is used.
%    3, a Neumann condition is used.
%
%    Input, integer VARIABLE_NUM, the number of variables.
%
%    Input, real NODE_C(VARIABLE_NUM), the finite element
%    coefficient vector.
%
%    Input, real NODE_R(VARIABLE_NUM), the residual vector.
%
%    Output, real NODE_R(VARIABLE_NUM), the adjusted residual.
%
  DIRICHLET = 2;

  [ u_bc, v_bc, p_bc ] = dirichlet_condition ( node_num, node_xy );

  for node = 1 : node_num

    iu = node_u_variable(node);
    iv = node_v_variable(node);
    ip = node_p_variable(node);

    if ( node_u_condition(node) == DIRICHLET )
      node_r(iu) = node_c(iu) - u_bc(node);
    end

    if ( node_v_condition(node) == DIRICHLET )
      node_r(iv) = node_c(iv) - v_bc(node);
    end

    if ( 0 < ip )
      if ( node_p_condition(node) == DIRICHLET )
        node_r(ip) = node_c(ip) - p_bc(node);
      end
    end

  end

  return
end