relax.c

LPARX is a C++ class library for for implementing portable scientific applications on distributed me

#include "redblack2d.h"

//
// Fortran name mangling is architecture-specific, so define a mangled
// name appropriate to your architecture
//

#if (defined(nCUBE2) || defined(CRAYC90))
#define redblack5 REDBLACK5
#define residual5 RESIDUAL5
#else
#define redblack5 redblack5_
#define residual5 residual5_
#endif

extern "C" {
void redblack5(double *u,
               const int *const nl, const int *const nh,
               const double *h, const int *const offset, double *du);

}

double relax(Grid2(double)& U, const double& h)
  {
   /*
      Call a Fortran routine to perform relaxation on the grid.

      This is an example of the C++ - Fortran interface. The C++
      grid class uses Fortran-style array ordering of the indices.
      So, to call Fortran, we need to pass the beginning of the
      grid array and also the x and y dimensions of the array. 

      The member function X.extents(Y), where X is a Region,
      returns the size of the Yth dimension of the Region object
      X. The member function X.data(), where X is a grid,
      returns a pointer the buffer holding the grid data of object X.

      Remember the parameter passing conventions in Fortran --
      use pointers to scalars. redblack5 is a Fortran subroutine
      that performs a red-black jacobi update on a 2D array
      of REAL*8 values (see file rb5.F).
   */

   const int red = 0, black = 1;
   double r0=0.0, r1=0.0;
   Region2 interior = grow(U.region(), -1);
   const Point2 nl = interior.lower();
   const Point2 nh = interior.upper();
   redblack5(U.data(), nl, nh, &h, &red, &r0);
   redblack5(U.data(), nl, nh, &h, &black, &r1);
   if (r1 > r0) r0 = r1;
   return(r0);
  }