xref: /petsc/src/dm/impls/da/hypre/mhyp.c (revision d94fc0b6cf22a878497ee22bbf61333f8d21cfbe)

/*
    Creates hypre ijmatrix from PETSc matrix
*/
#include <petscsys.h>
#include <petsc/private/matimpl.h>
#include <petscdmda.h>                /*I "petscdmda.h" I*/
#include <../src/dm/impls/da/hypre/mhyp.h>

/* -----------------------------------------------------------------------------------------------------------------*/

/*MC
   MATHYPRESTRUCT - MATHYPRESTRUCT = "hyprestruct" - A matrix type to be used for parallel sparse matrices
          based on the hypre HYPRE_StructMatrix.

   Level: intermediate

   Notes: Unlike the more general support for blocks in hypre this allows only one block per process and requires the block
          be defined by a DMDA.

          The matrix needs a DMDA associated with it by either a call to MatSetDM() or if the matrix is obtained from DMCreateMatrix()

.seealso: MatCreate(), PCPFMG, MatSetDM(), DMCreateMatrix()
M*/


PetscErrorCode  MatSetValuesLocal_HYPREStruct_3d(Mat mat,PetscInt nrow,const PetscInt irow[],PetscInt ncol,const PetscInt icol[],const PetscScalar y[],InsertMode addv)
{
  PetscErrorCode    ierr;
  PetscInt          i,j,stencil,index[3],row,entries[7];
  const PetscScalar *values = y;
  Mat_HYPREStruct   *ex     = (Mat_HYPREStruct*) mat->data;

  PetscFunctionBegin;
  if (PetscUnlikely(ncol > 7)) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"ncol %D > 7 too large",ncol);
  for (i=0; i<nrow; i++) {
    for (j=0; j<ncol; j++) {
      stencil = icol[j] - irow[i];
      if (!stencil) {
        entries[j] = 3;
      } else if (stencil == -1) {
        entries[j] = 2;
      } else if (stencil == 1) {
        entries[j] = 4;
      } else if (stencil == -ex->gnx) {
        entries[j] = 1;
      } else if (stencil == ex->gnx) {
        entries[j] = 5;
      } else if (stencil == -ex->gnxgny) {
        entries[j] = 0;
      } else if (stencil == ex->gnxgny) {
        entries[j] = 6;
      } else SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Local row %D local column %D have bad stencil %D",irow[i],icol[j],stencil);
    }
    row      = ex->gindices[irow[i]] - ex->rstart;
    index[0] = ex->xs + (row % ex->nx);
    index[1] = ex->ys + ((row/ex->nx) % ex->ny);
    index[2] = ex->zs + (row/(ex->nxny));
    if (addv == ADD_VALUES) {
      PetscStackCallStandard(HYPRE_StructMatrixAddToValues,(ex->hmat,(HYPRE_Int *)index,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
    } else {
      PetscStackCallStandard(HYPRE_StructMatrixSetValues,(ex->hmat,(HYPRE_Int *)index,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
    }
    values += ncol;
  }
  PetscFunctionReturn(0);
}

PetscErrorCode  MatZeroRowsLocal_HYPREStruct_3d(Mat mat,PetscInt nrow,const PetscInt irow[],PetscScalar d,Vec x,Vec b)
{
  PetscErrorCode  ierr;
  PetscInt        i,index[3],row,entries[7] = {0,1,2,3,4,5,6};
  PetscScalar     values[7];
  Mat_HYPREStruct *ex = (Mat_HYPREStruct*) mat->data;

  PetscFunctionBegin;
  if (x && b) SETERRQ(PetscObjectComm((PetscObject)mat),PETSC_ERR_SUP,"No support");
  ierr      = PetscMemzero(values,7*sizeof(PetscScalar));CHKERRQ(ierr);
  values[3] = d;
  for (i=0; i<nrow; i++) {
    row      = ex->gindices[irow[i]] - ex->rstart;
    index[0] = ex->xs + (row % ex->nx);
    index[1] = ex->ys + ((row/ex->nx) % ex->ny);
    index[2] = ex->zs + (row/(ex->nxny));
    PetscStackCallStandard(HYPRE_StructMatrixSetValues,(ex->hmat,(HYPRE_Int *)index,7,(HYPRE_Int *)entries,values));
  }
  PetscStackCallStandard(HYPRE_StructMatrixAssemble,(ex->hmat));
  PetscFunctionReturn(0);
}

PetscErrorCode MatZeroEntries_HYPREStruct_3d(Mat mat)
{
  PetscErrorCode  ierr;
  PetscInt        indices[7] = {0,1,2,3,4,5,6};
  Mat_HYPREStruct *ex        = (Mat_HYPREStruct*) mat->data;

  PetscFunctionBegin;
  /* hypre has no public interface to do this */
  PetscStackCallStandard(hypre_StructMatrixClearBoxValues,(ex->hmat,&ex->hbox,7,(HYPRE_Int *)indices,0,1));
  PetscStackCallStandard(HYPRE_StructMatrixAssemble,(ex->hmat));
  PetscFunctionReturn(0);
}

static PetscErrorCode  MatSetUp_HYPREStruct(Mat mat)
{
  PetscErrorCode         ierr;
  Mat_HYPREStruct        *ex = (Mat_HYPREStruct*) mat->data;
  PetscInt               dim,dof,sw[6],nx,ny,nz,ilower[3],iupper[3],ssize,i;
  DMBoundaryType         px,py,pz;
  DMDAStencilType        st;
  ISLocalToGlobalMapping ltog;
  DM                     da;

  PetscFunctionBegin;
  ierr   = MatGetDM(mat,(DM*)&da);CHKERRQ(ierr);
  ex->da = da;
  ierr   = PetscObjectReference((PetscObject)da);CHKERRQ(ierr);

  ierr       = DMDAGetInfo(ex->da,&dim,0,0,0,0,0,0,&dof,&sw[0],&px,&py,&pz,&st);CHKERRQ(ierr);
  ierr       = DMDAGetCorners(ex->da,&ilower[0],&ilower[1],&ilower[2],&iupper[0],&iupper[1],&iupper[2]);CHKERRQ(ierr);
  iupper[0] += ilower[0] - 1;
  iupper[1] += ilower[1] - 1;
  iupper[2] += ilower[2] - 1;

  /* the hypre_Box is used to zero out the matrix entries in MatZeroValues() */
  ex->hbox.imin[0] = ilower[0];
  ex->hbox.imin[1] = ilower[1];
  ex->hbox.imin[2] = ilower[2];
  ex->hbox.imax[0] = iupper[0];
  ex->hbox.imax[1] = iupper[1];
  ex->hbox.imax[2] = iupper[2];

  /* create the hypre grid object and set its information */
  if (dof > 1) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Currently only support for scalar problems");
  if (px || py || pz) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add periodic support by calling HYPRE_StructGridSetPeriodic()");
  PetscStackCallStandard(HYPRE_StructGridCreate,(ex->hcomm,dim,&ex->hgrid));
  PetscStackCallStandard(HYPRE_StructGridSetExtents,(ex->hgrid,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper));
  PetscStackCallStandard(HYPRE_StructGridAssemble,(ex->hgrid));

  sw[5] = sw[4] = sw[3] = sw[2] = sw[1] = sw[0];
  PetscStackCallStandard(HYPRE_StructGridSetNumGhost,(ex->hgrid,(HYPRE_Int *)sw));

  /* create the hypre stencil object and set its information */
  if (sw[0] > 1) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add support for wider stencils");
  if (st == DMDA_STENCIL_BOX) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add support for box stencils");
  if (dim == 1) {
    PetscInt offsets[3][1] = {{-1},{0},{1}};
    ssize = 3;
    PetscStackCallStandard(HYPRE_StructStencilCreate,(dim,ssize,&ex->hstencil));
    for (i=0; i<ssize; i++) {
      PetscStackCallStandard(HYPRE_StructStencilSetElement,(ex->hstencil,i,(HYPRE_Int *)offsets[i]));
    }
  } else if (dim == 2) {
    PetscInt offsets[5][2] = {{0,-1},{-1,0},{0,0},{1,0},{0,1}};
    ssize = 5;
    PetscStackCallStandard(HYPRE_StructStencilCreate,(dim,ssize,&ex->hstencil));
    for (i=0; i<ssize; i++) {
      PetscStackCallStandard(HYPRE_StructStencilSetElement,(ex->hstencil,i,(HYPRE_Int *)offsets[i]));
    }
  } else if (dim == 3) {
    PetscInt offsets[7][3] = {{0,0,-1},{0,-1,0},{-1,0,0},{0,0,0},{1,0,0},{0,1,0},{0,0,1}};
    ssize = 7;
    PetscStackCallStandard(HYPRE_StructStencilCreate,(dim,ssize,&ex->hstencil));
    for (i=0; i<ssize; i++) {
      PetscStackCallStandard(HYPRE_StructStencilSetElement,(ex->hstencil,i,(HYPRE_Int *)offsets[i]));
    }
  }

  /* create the HYPRE vector for rhs and solution */
  PetscStackCallStandard(HYPRE_StructVectorCreate,(ex->hcomm,ex->hgrid,&ex->hb));
  PetscStackCallStandard(HYPRE_StructVectorCreate,(ex->hcomm,ex->hgrid,&ex->hx));
  PetscStackCallStandard(HYPRE_StructVectorInitialize,(ex->hb));
  PetscStackCallStandard(HYPRE_StructVectorInitialize,(ex->hx));
  PetscStackCallStandard(HYPRE_StructVectorAssemble,(ex->hb));
  PetscStackCallStandard(HYPRE_StructVectorAssemble,(ex->hx));

  /* create the hypre matrix object and set its information */
  PetscStackCallStandard(HYPRE_StructMatrixCreate,(ex->hcomm,ex->hgrid,ex->hstencil,&ex->hmat));
  PetscStackCallStandard(HYPRE_StructGridDestroy,(ex->hgrid));
  PetscStackCallStandard(HYPRE_StructStencilDestroy,(ex->hstencil));
  if (ex->needsinitialization) {
    PetscStackCallStandard(HYPRE_StructMatrixInitialize,(ex->hmat));
    ex->needsinitialization = PETSC_FALSE;
  }

  /* set the global and local sizes of the matrix */
  ierr = DMDAGetCorners(da,0,0,0,&nx,&ny,&nz);CHKERRQ(ierr);
  ierr = MatSetSizes(mat,dof*nx*ny*nz,dof*nx*ny*nz,PETSC_DECIDE,PETSC_DECIDE);CHKERRQ(ierr);
  ierr = PetscLayoutSetBlockSize(mat->rmap,1);CHKERRQ(ierr);
  ierr = PetscLayoutSetBlockSize(mat->cmap,1);CHKERRQ(ierr);
  ierr = PetscLayoutSetUp(mat->rmap);CHKERRQ(ierr);
  ierr = PetscLayoutSetUp(mat->cmap);CHKERRQ(ierr);
  mat->preallocated = PETSC_TRUE;

  if (dim == 3) {
    mat->ops->setvalueslocal = MatSetValuesLocal_HYPREStruct_3d;
    mat->ops->zerorowslocal  = MatZeroRowsLocal_HYPREStruct_3d;
    mat->ops->zeroentries    = MatZeroEntries_HYPREStruct_3d;

    /*        ierr = MatZeroEntries_HYPREStruct_3d(mat);CHKERRQ(ierr); */
  } else SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Only support for 3d DMDA currently");

  /* get values that will be used repeatedly in MatSetValuesLocal() and MatZeroRowsLocal() repeatedly */
  ierr        = MatGetOwnershipRange(mat,&ex->rstart,NULL);CHKERRQ(ierr);
  ierr        = DMGetLocalToGlobalMapping(ex->da,&ltog);CHKERRQ(ierr);
  ierr        = ISLocalToGlobalMappingGetIndices(ltog, (const PetscInt **) &ex->gindices);CHKERRQ(ierr);
  ierr        = DMDAGetGhostCorners(ex->da,0,0,0,&ex->gnx,&ex->gnxgny,0);CHKERRQ(ierr);
  ex->gnxgny *= ex->gnx;
  ierr        = DMDAGetCorners(ex->da,&ex->xs,&ex->ys,&ex->zs,&ex->nx,&ex->ny,0);CHKERRQ(ierr);
  ex->nxny    = ex->nx*ex->ny;
  PetscFunctionReturn(0);
}

PetscErrorCode MatMult_HYPREStruct(Mat A,Vec x,Vec y)
{
  PetscErrorCode    ierr;
  const PetscScalar *xx;
  PetscScalar       *yy;
  PetscInt          ilower[3],iupper[3];
  Mat_HYPREStruct   *mx = (Mat_HYPREStruct*)(A->data);

  PetscFunctionBegin;
  ierr = DMDAGetCorners(mx->da,&ilower[0],&ilower[1],&ilower[2],&iupper[0],&iupper[1],&iupper[2]);CHKERRQ(ierr);

  iupper[0] += ilower[0] - 1;
  iupper[1] += ilower[1] - 1;
  iupper[2] += ilower[2] - 1;

  /* copy x values over to hypre */
  PetscStackCallStandard(HYPRE_StructVectorSetConstantValues,(mx->hb,0.0));
  ierr = VecGetArrayRead(x,&xx);CHKERRQ(ierr);
  PetscStackCallStandard(HYPRE_StructVectorSetBoxValues,(mx->hb,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,(PetscScalar*)xx));
  ierr = VecRestoreArrayRead(x,&xx);CHKERRQ(ierr);
  PetscStackCallStandard(HYPRE_StructVectorAssemble,(mx->hb));
  PetscStackCallStandard(HYPRE_StructMatrixMatvec,(1.0,mx->hmat,mx->hb,0.0,mx->hx));

  /* copy solution values back to PETSc */
  ierr = VecGetArray(y,&yy);CHKERRQ(ierr);
  PetscStackCallStandard(HYPRE_StructVectorGetBoxValues,(mx->hx,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,yy));
  ierr = VecRestoreArray(y,&yy);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PetscErrorCode MatAssemblyEnd_HYPREStruct(Mat mat,MatAssemblyType mode)
{
  Mat_HYPREStruct *ex = (Mat_HYPREStruct*) mat->data;
  PetscErrorCode  ierr;

  PetscFunctionBegin;
  PetscStackCallStandard(HYPRE_StructMatrixAssemble,(ex->hmat));
  /* PetscStackCallStandard(HYPRE_StructMatrixPrint,("dummy",ex->hmat,0)); */
  PetscFunctionReturn(0);
}

PetscErrorCode MatZeroEntries_HYPREStruct(Mat mat)
{
  PetscFunctionBegin;
  /* before the DMDA is set to the matrix the zero doesn't need to do anything */
  PetscFunctionReturn(0);
}

PetscErrorCode MatDestroy_HYPREStruct(Mat mat)
{
  Mat_HYPREStruct *ex = (Mat_HYPREStruct*) mat->data;
  PetscErrorCode  ierr;

  PetscFunctionBegin;
  PetscStackCallStandard(HYPRE_StructMatrixDestroy,(ex->hmat));
  PetscStackCallStandard(HYPRE_StructVectorDestroy,(ex->hx));
  PetscStackCallStandard(HYPRE_StructVectorDestroy,(ex->hb));
  ierr = PetscObjectDereference((PetscObject)ex->da);CHKERRQ(ierr);
  ierr = MPI_Comm_free(&(ex->hcomm));CHKERRQ(ierr);
  ierr = PetscFree(ex);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PETSC_EXTERN PetscErrorCode MatCreate_HYPREStruct(Mat B)
{
  Mat_HYPREStruct *ex;
  PetscErrorCode  ierr;

  PetscFunctionBegin;
  ierr         = PetscNewLog(B,&ex);CHKERRQ(ierr);
  B->data      = (void*)ex;
  B->rmap->bs  = 1;
  B->assembled = PETSC_FALSE;

  B->insertmode = NOT_SET_VALUES;

  B->ops->assemblyend = MatAssemblyEnd_HYPREStruct;
  B->ops->mult        = MatMult_HYPREStruct;
  B->ops->zeroentries = MatZeroEntries_HYPREStruct;
  B->ops->destroy     = MatDestroy_HYPREStruct;
  B->ops->setup       = MatSetUp_HYPREStruct;

  ex->needsinitialization = PETSC_TRUE;

  ierr = MPI_Comm_dup(PetscObjectComm((PetscObject)B),&(ex->hcomm));CHKERRQ(ierr);
  ierr = PetscObjectChangeTypeName((PetscObject)B,MATHYPRESTRUCT);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

/*MC
   MATHYPRESSTRUCT - MATHYPRESSTRUCT = "hypresstruct" - A matrix type to be used for parallel sparse matrices
          based on the hypre HYPRE_SStructMatrix.


   Level: intermediate

   Notes: Unlike hypre's general semi-struct object consisting of a collection of structured-grid objects and unstructured
          grid objects, we restrict the semi-struct objects to consist of only structured-grid components.

          Unlike the more general support for parts and blocks in hypre this allows only one part, and one block per process and requires the block
          be defined by a DMDA.

          The matrix needs a DMDA associated with it by either a call to MatSetDM() or if the matrix is obtained from DMCreateMatrix()

M*/

PetscErrorCode  MatSetValuesLocal_HYPRESStruct_3d(Mat mat,PetscInt nrow,const PetscInt irow[],PetscInt ncol,const PetscInt icol[],const PetscScalar y[],InsertMode addv)
{
  PetscErrorCode    ierr;
  PetscInt          i,j,stencil,index[3];
  const PetscScalar *values = y;
  Mat_HYPRESStruct  *ex     = (Mat_HYPRESStruct*) mat->data;

  PetscInt          part = 0;          /* Petsc sstruct interface only allows 1 part */
  PetscInt          ordering;
  PetscInt          grid_rank, to_grid_rank;
  PetscInt          var_type, to_var_type;
  PetscInt          to_var_entry = 0;
  PetscInt          nvars= ex->nvars;
  PetscInt          row,*entries;

  PetscFunctionBegin;
  ierr     = PetscMalloc1(7*nvars,&entries);CHKERRQ(ierr);
  ordering = ex->dofs_order;  /* ordering= 0   nodal ordering
                                           1   variable ordering */
  /* stencil entries are ordered by variables: var0_stencil0, var0_stencil1, ..., var0_stencil6, var1_stencil0, var1_stencil1, ...  */
  if (!ordering) {
    for (i=0; i<nrow; i++) {
      grid_rank= irow[i]/nvars;
      var_type = (irow[i] % nvars);

      for (j=0; j<ncol; j++) {
        to_grid_rank= icol[j]/nvars;
        to_var_type = (icol[j] % nvars);

        to_var_entry= to_var_entry*7;
        entries[j]  = to_var_entry;

        stencil = to_grid_rank-grid_rank;
        if (!stencil) {
          entries[j] += 3;
        } else if (stencil == -1) {
          entries[j] += 2;
        } else if (stencil == 1) {
          entries[j] += 4;
        } else if (stencil == -ex->gnx) {
          entries[j] += 1;
        } else if (stencil == ex->gnx) {
          entries[j] += 5;
        } else if (stencil == -ex->gnxgny) {
          entries[j] += 0;
        } else if (stencil == ex->gnxgny) {
          entries[j] += 6;
        } else SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Local row %D local column %D have bad stencil %D",irow[i],icol[j],stencil);
      }

      row      = ex->gindices[grid_rank] - ex->rstart;
      index[0] = ex->xs + (row % ex->nx);
      index[1] = ex->ys + ((row/ex->nx) % ex->ny);
      index[2] = ex->zs + (row/(ex->nxny));

      if (addv == ADD_VALUES) {
        PetscStackCallStandard(HYPRE_SStructMatrixAddToValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
      } else {
        PetscStackCallStandard(HYPRE_SStructMatrixSetValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
      }
      values += ncol;
    }
  } else {
    for (i=0; i<nrow; i++) {
      var_type = irow[i]/(ex->gnxgnygnz);
      grid_rank= irow[i] - var_type*(ex->gnxgnygnz);

      for (j=0; j<ncol; j++) {
        to_var_type = icol[j]/(ex->gnxgnygnz);
        to_grid_rank= icol[j] - to_var_type*(ex->gnxgnygnz);

        to_var_entry= to_var_entry*7;
        entries[j]  = to_var_entry;

        stencil = to_grid_rank-grid_rank;
        if (!stencil) {
          entries[j] += 3;
        } else if (stencil == -1) {
          entries[j] += 2;
        } else if (stencil == 1) {
          entries[j] += 4;
        } else if (stencil == -ex->gnx) {
          entries[j] += 1;
        } else if (stencil == ex->gnx) {
          entries[j] += 5;
        } else if (stencil == -ex->gnxgny) {
          entries[j] += 0;
        } else if (stencil == ex->gnxgny) {
          entries[j] += 6;
        } else SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Local row %D local column %D have bad stencil %D",irow[i],icol[j],stencil);
      }

      row      = ex->gindices[grid_rank] - ex->rstart;
      index[0] = ex->xs + (row % ex->nx);
      index[1] = ex->ys + ((row/ex->nx) % ex->ny);
      index[2] = ex->zs + (row/(ex->nxny));

      if (addv == ADD_VALUES) {
        PetscStackCallStandard(HYPRE_SStructMatrixAddToValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
      } else {
        PetscStackCallStandard(HYPRE_SStructMatrixSetValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,ncol,(HYPRE_Int *)entries,(PetscScalar*)values));
      }
      values += ncol;
    }
  }
  ierr = PetscFree(entries);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PetscErrorCode  MatZeroRowsLocal_HYPRESStruct_3d(Mat mat,PetscInt nrow,const PetscInt irow[],PetscScalar d,Vec x,Vec b)
{
  PetscErrorCode   ierr;
  PetscInt         i,index[3];
  PetscScalar      **values;
  Mat_HYPRESStruct *ex = (Mat_HYPRESStruct*) mat->data;

  PetscInt         part     = 0;      /* Petsc sstruct interface only allows 1 part */
  PetscInt         ordering = ex->dofs_order;
  PetscInt         grid_rank;
  PetscInt         var_type;
  PetscInt         nvars= ex->nvars;
  PetscInt         row,*entries;

  PetscFunctionBegin;
  if (x && b) SETERRQ(PetscObjectComm((PetscObject)mat),PETSC_ERR_SUP,"No support");
  ierr = PetscMalloc1(7*nvars,&entries);CHKERRQ(ierr);

  ierr = PetscMalloc1(nvars,&values);CHKERRQ(ierr);
  ierr = PetscMalloc1(7*nvars*nvars,&values[0]);CHKERRQ(ierr);
  for (i=1; i<nvars; i++) {
    values[i] = values[i-1] + nvars*7;
  }

  for (i=0; i< nvars; i++) {
    ierr           = PetscMemzero(values[i],nvars*7*sizeof(PetscScalar));CHKERRQ(ierr);
    *(values[i]+3) = d;
  }

  for (i= 0; i< nvars*7; i++) entries[i] = i;

  if (!ordering) {
    for (i=0; i<nrow; i++) {
      grid_rank = irow[i] / nvars;
      var_type  =(irow[i] % nvars);

      row      = ex->gindices[grid_rank] - ex->rstart;
      index[0] = ex->xs + (row % ex->nx);
      index[1] = ex->ys + ((row/ex->nx) % ex->ny);
      index[2] = ex->zs + (row/(ex->nxny));
      PetscStackCallStandard(HYPRE_SStructMatrixSetValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,7*nvars,(HYPRE_Int *)entries,values[var_type]));
    }
  } else {
    for (i=0; i<nrow; i++) {
      var_type = irow[i]/(ex->gnxgnygnz);
      grid_rank= irow[i] - var_type*(ex->gnxgnygnz);

      row      = ex->gindices[grid_rank] - ex->rstart;
      index[0] = ex->xs + (row % ex->nx);
      index[1] = ex->ys + ((row/ex->nx) % ex->ny);
      index[2] = ex->zs + (row/(ex->nxny));
      PetscStackCallStandard(HYPRE_SStructMatrixSetValues,(ex->ss_mat,part,(HYPRE_Int *)index,var_type,7*nvars,(HYPRE_Int *)entries,values[var_type]));
    }
  }
  PetscStackCallStandard(HYPRE_SStructMatrixAssemble,(ex->ss_mat));
  ierr = PetscFree(values[0]);CHKERRQ(ierr);
  ierr = PetscFree(values);CHKERRQ(ierr);
  ierr = PetscFree(entries);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PetscErrorCode MatZeroEntries_HYPRESStruct_3d(Mat mat)
{
  PetscErrorCode   ierr;
  Mat_HYPRESStruct *ex  = (Mat_HYPRESStruct*) mat->data;
  PetscInt         nvars= ex->nvars;
  PetscInt         size;
  PetscInt         part= 0;   /* only one part */

  PetscFunctionBegin;
  size = ((ex->hbox.imax[0])-(ex->hbox.imin[0])+1)*((ex->hbox.imax[1])-(ex->hbox.imin[1])+1)*((ex->hbox.imax[2])-(ex->hbox.imin[2])+1);
  {
    PetscInt    i,*entries,iupper[3],ilower[3];
    PetscScalar *values;


    for (i= 0; i< 3; i++) {
      ilower[i]= ex->hbox.imin[i];
      iupper[i]= ex->hbox.imax[i];
    }

    ierr = PetscMalloc2(nvars*7,&entries,nvars*7*size,&values);CHKERRQ(ierr);
    for (i= 0; i< nvars*7; i++) entries[i]= i;
    ierr = PetscMemzero(values,nvars*7*size*sizeof(PetscScalar));CHKERRQ(ierr);

    for (i= 0; i< nvars; i++) {
      PetscStackCallStandard(HYPRE_SStructMatrixSetBoxValues,(ex->ss_mat,part,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,i,nvars*7,(HYPRE_Int *)entries,values));
    }
    ierr = PetscFree2(entries,values);CHKERRQ(ierr);
  }
  PetscStackCallStandard(HYPRE_SStructMatrixAssemble,(ex->ss_mat));
  PetscFunctionReturn(0);
}


static PetscErrorCode  MatSetUp_HYPRESStruct(Mat mat)
{
  PetscErrorCode         ierr;
  Mat_HYPRESStruct       *ex = (Mat_HYPRESStruct*) mat->data;
  PetscInt               dim,dof,sw[3],nx,ny,nz;
  PetscInt               ilower[3],iupper[3],ssize,i;
  DMBoundaryType         px,py,pz;
  DMDAStencilType        st;
  PetscInt               nparts= 1;  /* assuming only one part */
  PetscInt               part  = 0;
  ISLocalToGlobalMapping ltog;
  DM                     da;

  PetscFunctionBegin;
  ierr   = MatGetDM(mat,(DM*)&da);CHKERRQ(ierr);
  ex->da = da;
  ierr   = PetscObjectReference((PetscObject)da);CHKERRQ(ierr);

  ierr       = DMDAGetInfo(ex->da,&dim,0,0,0,0,0,0,&dof,&sw[0],&px,&py,&pz,&st);CHKERRQ(ierr);
  ierr       = DMDAGetCorners(ex->da,&ilower[0],&ilower[1],&ilower[2],&iupper[0],&iupper[1],&iupper[2]);CHKERRQ(ierr);
  iupper[0] += ilower[0] - 1;
  iupper[1] += ilower[1] - 1;
  iupper[2] += ilower[2] - 1;
  /* the hypre_Box is used to zero out the matrix entries in MatZeroValues() */
  ex->hbox.imin[0] = ilower[0];
  ex->hbox.imin[1] = ilower[1];
  ex->hbox.imin[2] = ilower[2];
  ex->hbox.imax[0] = iupper[0];
  ex->hbox.imax[1] = iupper[1];
  ex->hbox.imax[2] = iupper[2];

  ex->dofs_order = 0;

  /* assuming that the same number of dofs on each gridpoint. Also assume all cell-centred based */
  ex->nvars= dof;

  /* create the hypre grid object and set its information */
  if (px || py || pz) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add periodic support by calling HYPRE_SStructGridSetPeriodic()");
  PetscStackCallStandard(HYPRE_SStructGridCreate,(ex->hcomm,dim,nparts,&ex->ss_grid));
  PetscStackCallStandard(HYPRE_SStructGridSetExtents,(ex->ss_grid,part,ex->hbox.imin,ex->hbox.imax));
  {
    HYPRE_SStructVariable *vartypes;
    ierr = PetscMalloc1(ex->nvars,&vartypes);CHKERRQ(ierr);
    for (i= 0; i< ex->nvars; i++) vartypes[i]= HYPRE_SSTRUCT_VARIABLE_CELL;
    PetscStackCallStandard(HYPRE_SStructGridSetVariables,(ex->ss_grid, part, ex->nvars,vartypes));
    ierr = PetscFree(vartypes);CHKERRQ(ierr);
  }
  PetscStackCallStandard(HYPRE_SStructGridAssemble,(ex->ss_grid));

  sw[1] = sw[0];
  sw[2] = sw[1];
  /* PetscStackCallStandard(HYPRE_SStructGridSetNumGhost,(ex->ss_grid,sw)); */

  /* create the hypre stencil object and set its information */
  if (sw[0] > 1) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add support for wider stencils");
  if (st == DMDA_STENCIL_BOX) SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Ask us to add support for box stencils");

  if (dim == 1) {
    PetscInt offsets[3][1] = {{-1},{0},{1}};
    PetscInt j, cnt;

    ssize = 3*(ex->nvars);
    PetscStackCallStandard(HYPRE_SStructStencilCreate,(dim,ssize,&ex->ss_stencil));
    cnt= 0;
    for (i = 0; i < (ex->nvars); i++) {
      for (j = 0; j < 3; j++) {
        PetscStackCallStandard(HYPRE_SStructStencilSetEntry,(ex->ss_stencil, cnt, (HYPRE_Int *)offsets[j], i));
        cnt++;
      }
    }
  } else if (dim == 2) {
    PetscInt offsets[5][2] = {{0,-1},{-1,0},{0,0},{1,0},{0,1}};
    PetscInt j, cnt;

    ssize = 5*(ex->nvars);
    PetscStackCallStandard(HYPRE_SStructStencilCreate,(dim,ssize,&ex->ss_stencil));
    cnt= 0;
    for (i= 0; i< (ex->nvars); i++) {
      for (j= 0; j< 5; j++) {
        PetscStackCallStandard(HYPRE_SStructStencilSetEntry,(ex->ss_stencil, cnt, (HYPRE_Int *)offsets[j], i));
        cnt++;
      }
    }
  } else if (dim == 3) {
    PetscInt offsets[7][3] = {{0,0,-1},{0,-1,0},{-1,0,0},{0,0,0},{1,0,0},{0,1,0},{0,0,1}};
    PetscInt j, cnt;

    ssize = 7*(ex->nvars);
    PetscStackCallStandard(HYPRE_SStructStencilCreate,(dim,ssize,&ex->ss_stencil));
    cnt= 0;
    for (i= 0; i< (ex->nvars); i++) {
      for (j= 0; j< 7; j++) {
        PetscStackCallStandard(HYPRE_SStructStencilSetEntry,(ex->ss_stencil, cnt, (HYPRE_Int *)offsets[j], i));
        cnt++;
      }
    }
  }

  /* create the HYPRE graph */
  PetscStackCallStandard(HYPRE_SStructGraphCreate,(ex->hcomm, ex->ss_grid, &(ex->ss_graph)));

  /* set the stencil graph. Note that each variable has the same graph. This means that each
     variable couples to all the other variable and with the same stencil pattern. */
  for (i= 0; i< (ex->nvars); i++) {
    PetscStackCallStandard(HYPRE_SStructGraphSetStencil,(ex->ss_graph,part,i,ex->ss_stencil));
  }
  PetscStackCallStandard(HYPRE_SStructGraphAssemble,(ex->ss_graph));

  /* create the HYPRE sstruct vectors for rhs and solution */
  PetscStackCallStandard(HYPRE_SStructVectorCreate,(ex->hcomm,ex->ss_grid,&ex->ss_b));
  PetscStackCallStandard(HYPRE_SStructVectorCreate,(ex->hcomm,ex->ss_grid,&ex->ss_x));
  PetscStackCallStandard(HYPRE_SStructVectorInitialize,(ex->ss_b));
  PetscStackCallStandard(HYPRE_SStructVectorInitialize,(ex->ss_x));
  PetscStackCallStandard(HYPRE_SStructVectorAssemble,(ex->ss_b));
  PetscStackCallStandard(HYPRE_SStructVectorAssemble,(ex->ss_x));

  /* create the hypre matrix object and set its information */
  PetscStackCallStandard(HYPRE_SStructMatrixCreate,(ex->hcomm,ex->ss_graph,&ex->ss_mat));
  PetscStackCallStandard(HYPRE_SStructGridDestroy,(ex->ss_grid));
  PetscStackCallStandard(HYPRE_SStructStencilDestroy,(ex->ss_stencil));
  if (ex->needsinitialization) {
    PetscStackCallStandard(HYPRE_SStructMatrixInitialize,(ex->ss_mat));
    ex->needsinitialization = PETSC_FALSE;
  }

  /* set the global and local sizes of the matrix */
  ierr = DMDAGetCorners(da,0,0,0,&nx,&ny,&nz);CHKERRQ(ierr);
  ierr = MatSetSizes(mat,dof*nx*ny*nz,dof*nx*ny*nz,PETSC_DECIDE,PETSC_DECIDE);CHKERRQ(ierr);
  ierr = PetscLayoutSetBlockSize(mat->rmap,dof);CHKERRQ(ierr);
  ierr = PetscLayoutSetBlockSize(mat->cmap,dof);CHKERRQ(ierr);
  ierr = PetscLayoutSetUp(mat->rmap);CHKERRQ(ierr);
  ierr = PetscLayoutSetUp(mat->cmap);CHKERRQ(ierr);
  mat->preallocated = PETSC_TRUE;

  if (dim == 3) {
    mat->ops->setvalueslocal = MatSetValuesLocal_HYPRESStruct_3d;
    mat->ops->zerorowslocal  = MatZeroRowsLocal_HYPRESStruct_3d;
    mat->ops->zeroentries    = MatZeroEntries_HYPRESStruct_3d;

    /* ierr = MatZeroEntries_HYPRESStruct_3d(mat);CHKERRQ(ierr); */
  } else SETERRQ(PetscObjectComm((PetscObject)da),PETSC_ERR_SUP,"Only support for 3d DMDA currently");

  /* get values that will be used repeatedly in MatSetValuesLocal() and MatZeroRowsLocal() repeatedly */
  ierr = MatGetOwnershipRange(mat,&ex->rstart,NULL);CHKERRQ(ierr);
  ierr = DMGetLocalToGlobalMapping(ex->da,&ltog);CHKERRQ(ierr);
  ierr = ISLocalToGlobalMappingGetIndices(ltog, (const PetscInt **) &ex->gindices);CHKERRQ(ierr);
  ierr = DMDAGetGhostCorners(ex->da,0,0,0,&ex->gnx,&ex->gnxgny,&ex->gnxgnygnz);CHKERRQ(ierr);

  ex->gnxgny    *= ex->gnx;
  ex->gnxgnygnz *= ex->gnxgny;

  ierr = DMDAGetCorners(ex->da,&ex->xs,&ex->ys,&ex->zs,&ex->nx,&ex->ny,&ex->nz);CHKERRQ(ierr);

  ex->nxny   = ex->nx*ex->ny;
  ex->nxnynz = ex->nz*ex->nxny;
  PetscFunctionReturn(0);
}

PetscErrorCode MatMult_HYPRESStruct(Mat A,Vec x,Vec y)
{
  PetscErrorCode    ierr;
  const PetscScalar *xx;
  PetscScalar       *yy;
  PetscInt          ilower[3],iupper[3];
  Mat_HYPRESStruct  *mx     = (Mat_HYPRESStruct*)(A->data);
  PetscInt          ordering= mx->dofs_order;
  PetscInt          nvars   = mx->nvars;
  PetscInt          part    = 0;
  PetscInt          size;
  PetscInt          i;

  PetscFunctionBegin;
  ierr       = DMDAGetCorners(mx->da,&ilower[0],&ilower[1],&ilower[2],&iupper[0],&iupper[1],&iupper[2]);CHKERRQ(ierr);
  iupper[0] += ilower[0] - 1;
  iupper[1] += ilower[1] - 1;
  iupper[2] += ilower[2] - 1;

  size= 1;
  for (i = 0; i < 3; i++) size *= (iupper[i]-ilower[i]+1);

  /* copy x values over to hypre for variable ordering */
  if (ordering) {
    PetscStackCallStandard(HYPRE_SStructVectorSetConstantValues,(mx->ss_b,0.0));
    ierr = VecGetArrayRead(x,&xx);CHKERRQ(ierr);
    for (i= 0; i< nvars; i++) {
      PetscStackCallStandard(HYPRE_SStructVectorSetBoxValues,(mx->ss_b,part,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,i,(PetscScalar*)xx+(size*i)));
    }
    ierr = VecRestoreArrayRead(x,&xx);CHKERRQ(ierr);
    PetscStackCallStandard(HYPRE_SStructVectorAssemble,(mx->ss_b));
    PetscStackCallStandard(HYPRE_SStructMatrixMatvec,(1.0,mx->ss_mat,mx->ss_b,0.0,mx->ss_x));

    /* copy solution values back to PETSc */
    ierr = VecGetArray(y,&yy);CHKERRQ(ierr);
    for (i= 0; i< nvars; i++) {
      PetscStackCallStandard(HYPRE_SStructVectorGetBoxValues,(mx->ss_x,part,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,i,yy+(size*i)));
    }
    ierr = VecRestoreArray(y,&yy);CHKERRQ(ierr);
  } else {      /* nodal ordering must be mapped to variable ordering for sys_pfmg */
    PetscScalar *z;
    PetscInt    j, k;

    ierr = PetscMalloc1(nvars*size,&z);CHKERRQ(ierr);
    PetscStackCallStandard(HYPRE_SStructVectorSetConstantValues,(mx->ss_b,0.0));
    ierr = VecGetArrayRead(x,&xx);CHKERRQ(ierr);

    /* transform nodal to hypre's variable ordering for sys_pfmg */
    for (i= 0; i< size; i++) {
      k= i*nvars;
      for (j= 0; j< nvars; j++) z[j*size+i]= xx[k+j];
    }
    for (i= 0; i< nvars; i++) {
      PetscStackCallStandard(HYPRE_SStructVectorSetBoxValues,(mx->ss_b,part,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,i,z+(size*i)));
    }
    ierr = VecRestoreArrayRead(x,&xx);CHKERRQ(ierr);
    PetscStackCallStandard(HYPRE_SStructVectorAssemble,(mx->ss_b));
    PetscStackCallStandard(HYPRE_SStructMatrixMatvec,(1.0,mx->ss_mat,mx->ss_b,0.0,mx->ss_x));

    /* copy solution values back to PETSc */
    ierr = VecGetArray(y,&yy);CHKERRQ(ierr);
    for (i= 0; i< nvars; i++) {
      PetscStackCallStandard(HYPRE_SStructVectorGetBoxValues,(mx->ss_x,part,(HYPRE_Int *)ilower,(HYPRE_Int *)iupper,i,z+(size*i)));
    }
    /* transform hypre's variable ordering for sys_pfmg to nodal ordering */
    for (i= 0; i< size; i++) {
      k= i*nvars;
      for (j= 0; j< nvars; j++) yy[k+j]= z[j*size+i];
    }
    ierr = VecRestoreArray(y,&yy);CHKERRQ(ierr);
    ierr = PetscFree(z);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

PetscErrorCode MatAssemblyEnd_HYPRESStruct(Mat mat,MatAssemblyType mode)
{
  Mat_HYPRESStruct *ex = (Mat_HYPRESStruct*) mat->data;
  PetscErrorCode   ierr;

  PetscFunctionBegin;
  PetscStackCallStandard(HYPRE_SStructMatrixAssemble,(ex->ss_mat));
  PetscFunctionReturn(0);
}

PetscErrorCode MatZeroEntries_HYPRESStruct(Mat mat)
{
  PetscFunctionBegin;
  /* before the DMDA is set to the matrix the zero doesn't need to do anything */
  PetscFunctionReturn(0);
}

PetscErrorCode MatDestroy_HYPRESStruct(Mat mat)
{
  Mat_HYPRESStruct       *ex = (Mat_HYPRESStruct*) mat->data;
  PetscErrorCode         ierr;
  ISLocalToGlobalMapping ltog;

  PetscFunctionBegin;
  ierr = DMGetLocalToGlobalMapping(ex->da,&ltog);CHKERRQ(ierr);
  ierr = ISLocalToGlobalMappingRestoreIndices(ltog, (const PetscInt **) &ex->gindices);CHKERRQ(ierr);
  PetscStackCallStandard(HYPRE_SStructGraphDestroy,(ex->ss_graph));
  PetscStackCallStandard(HYPRE_SStructMatrixDestroy,(ex->ss_mat));
  PetscStackCallStandard(HYPRE_SStructVectorDestroy,(ex->ss_x));
  PetscStackCallStandard(HYPRE_SStructVectorDestroy,(ex->ss_b));
  ierr = PetscObjectDereference((PetscObject)ex->da);CHKERRQ(ierr);
  ierr = MPI_Comm_free(&(ex->hcomm));CHKERRQ(ierr);
  ierr = PetscFree(ex);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PETSC_EXTERN PetscErrorCode MatCreate_HYPRESStruct(Mat B)
{
  Mat_HYPRESStruct *ex;
  PetscErrorCode   ierr;

  PetscFunctionBegin;
  ierr         = PetscNewLog(B,&ex);CHKERRQ(ierr);
  B->data      = (void*)ex;
  B->rmap->bs  = 1;
  B->assembled = PETSC_FALSE;

  B->insertmode = NOT_SET_VALUES;

  B->ops->assemblyend = MatAssemblyEnd_HYPRESStruct;
  B->ops->mult        = MatMult_HYPRESStruct;
  B->ops->zeroentries = MatZeroEntries_HYPRESStruct;
  B->ops->destroy     = MatDestroy_HYPRESStruct;
  B->ops->setup       = MatSetUp_HYPRESStruct;

  ex->needsinitialization = PETSC_TRUE;

  ierr = MPI_Comm_dup(PetscObjectComm((PetscObject)B),&(ex->hcomm));CHKERRQ(ierr);
  ierr = PetscObjectChangeTypeName((PetscObject)B,MATHYPRESSTRUCT);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}