Laplacian.cpp

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#include "CSR.hpp"

namespace SpMP
{

void generate3D27PtLaplacian(CSR *A, int nx, int ny, int nz, int base /*=0*/) {
  A->dealloc();

  A->m = A->n = nx*ny*nz;
  A->rowptr = MALLOC(int, A->m + 1);
  A->diagptr = MALLOC(int, A->m);
  A->idiag = MALLOC(double, A->m);
  A->diag = MALLOC(double, A->m);
  A->rowptr[0] = 0;

  int idx = 0;
//#define LOWER_TRIANGULAR
#ifdef LOWER_TRIANGULAR
  for (int iz = 0; iz < nz; ++iz) {
    for (int iy = 0; iy < ny; ++iy) {
      for (int ix = 0; ix < nx; ++ix) {
        int row = (iz*ny + iy)*nx + ix;

        for (int sz = -1; sz <= 1; ++sz) {
          if (iz + sz < 0 || iz + sz >= nz) continue;
          for (int sy = -1; sy <= 1; ++sy) {
            if (iy + sy < 0 || iy + sy >= ny) continue;
            for (int sx = -1; sx <= 1; ++sx) {
              if (ix + sx < 0 || ix + sx >= nx) continue;
              int col = row + (sz*ny + sy)*nx + sx;
              if (col > row) continue;
              ++idx;
            } //sx
          } // sy
        } // sz

        A->rowptr[row + 1] = idx;
      } // ix
    } // iy
  } // iz
#else
  for (int iz = 0; iz < nz; ++iz) {
    int dz = (iz >= 1 && iz < nz - 1) ? 3 : (nz == 1 ? 1 : 2);
    for (int iy = 0; iy < ny; ++iy) {
      int dy = ((iy >= 1 && iy < ny - 1) ? 3 : (nz == 1 ? 1 : 2))*dz;
      for (int ix = 0; ix < nx; ++ix) {
        int row = (iz*ny + iy)*nx + ix;

        int dx = (ix >= 1 && ix < nx - 1) ? 3 : (nz == 1 ? 1 : 2);
        idx += dx*dy;
        A->rowptr[row + 1] = idx;
      } // ix
    } // iy
  } // iz
#endif

  int nnz = idx;
  A->colidx = MALLOC(int, nnz);
  A->values = MALLOC(double, nnz);

#pragma omp parallel for collapse(2)
  for (int iz = 0; iz < nz; ++iz) {
    for (int iy = 0; iy < ny; ++iy) {
      int sz_begin = iz <= 0 ? 0 : -1;
      int sz_end = iz >= nz - 1 ? 0 : 1;

      int sy_begin = iy <= 0 ? 0 : -1;
      int sy_end = iy >= ny - 1 ? 0 : 1;
      for (int ix = 0; ix < nx; ++ix) {
        int sx_begin = ix <= 0 ? 0 : -1;
        int sx_end = ix >= nx - 1 ? 0 : 1;

        int row = (iz*ny + iy)*nx + ix;
        int idx = A->rowptr[row];

        for (int sz = sz_begin; sz <= sz_end; ++sz) {
          for (int sy = sy_begin; sy <= sy_end; ++sy) {
            for (int sx = sx_begin; sx <= sx_end; ++sx) {
              int col = row + (sz*ny + sy)*nx + sx;
#ifdef LOWER_TRIANGULAR
              if (col > row) continue;
#endif
              if (col == row) {
                A->diag[row] = 26.0;
                A->values[idx] = A->diag[row];
                A->idiag[row] = 1/A->diag[row];
                A->diagptr[row] = idx;
              }
              else {
                A->values[idx] = -1;
              }
              A->colidx[idx] = col;
              ++idx;
            } //sx
          } // sy
        } // sz
      } // ix
    } // iy
  } // iz

  if (1 == base) {
    A->make1BasedIndexing();
  }
  else {
    assert(0 == base);
  }

  assert(idx == nnz);
}

void generate3D27PtLaplacian(CSR *A, int n, int base /*=0*/) {
  generate3D27PtLaplacian(A, n, n, n, base);
}

} // namespace SpMP