xref: /petsc/src/ksp/pc/impls/vpbjacobi/vpbjacobi.c (revision 8a9c020ef9386a9599af7d232cee023eb5ec42c5)

/*
   Include files needed for the variable size block PBJacobi preconditioner:
     pcimpl.h - private include file intended for use by all preconditioners
*/

#include <petsc/private/pcimpl.h>   /*I "petscpc.h" I*/

/*
   Private context (data structure) for the VPBJacobi preconditioner.
*/
typedef struct {
  MatScalar *diag;
} PC_VPBJacobi;

static PetscErrorCode PCApply_VPBJacobi(PC pc,Vec x,Vec y)
{
  PC_VPBJacobi      *jac = (PC_VPBJacobi*)pc->data;
  PetscInt          i,ncnt = 0;
  const MatScalar   *diag = jac->diag;
  PetscInt          ib,jb,bs;
  const PetscScalar *xx;
  PetscScalar       *yy,x0,x1,x2,x3,x4,x5,x6;
  PetscInt          nblocks;
  const PetscInt    *bsizes;

  PetscFunctionBegin;
  PetscCall(MatGetVariableBlockSizes(pc->pmat,&nblocks,&bsizes));
  PetscCall(VecGetArrayRead(x,&xx));
  PetscCall(VecGetArray(y,&yy));
  for (i=0; i<nblocks; i++) {
    bs = bsizes[i];
    switch (bs) {
    case 1:
      yy[ncnt] = *diag*xx[ncnt];
      break;
    case 2:
      x0         = xx[ncnt]; x1 = xx[ncnt+1];
      yy[ncnt]   = diag[0]*x0 + diag[2]*x1;
      yy[ncnt+1] = diag[1]*x0 + diag[3]*x1;
      break;
    case 3:
      x0 = xx[ncnt]; x1 = xx[ncnt+1]; x2 = xx[ncnt+2];
      yy[ncnt]   = diag[0]*x0 + diag[3]*x1 + diag[6]*x2;
      yy[ncnt+1] = diag[1]*x0 + diag[4]*x1 + diag[7]*x2;
      yy[ncnt+2] = diag[2]*x0 + diag[5]*x1 + diag[8]*x2;
      break;
    case 4:
      x0 = xx[ncnt]; x1 = xx[ncnt+1]; x2 = xx[ncnt+2]; x3 = xx[ncnt+3];
      yy[ncnt]   = diag[0]*x0 + diag[4]*x1 + diag[8]*x2  + diag[12]*x3;
      yy[ncnt+1] = diag[1]*x0 + diag[5]*x1 + diag[9]*x2  + diag[13]*x3;
      yy[ncnt+2] = diag[2]*x0 + diag[6]*x1 + diag[10]*x2 + diag[14]*x3;
      yy[ncnt+3] = diag[3]*x0 + diag[7]*x1 + diag[11]*x2 + diag[15]*x3;
      break;
    case 5:
      x0 = xx[ncnt]; x1 = xx[ncnt+1]; x2 = xx[ncnt+2]; x3 = xx[ncnt+3]; x4 = xx[ncnt+4];
      yy[ncnt]   = diag[0]*x0 + diag[5]*x1 + diag[10]*x2  + diag[15]*x3 + diag[20]*x4;
      yy[ncnt+1] = diag[1]*x0 + diag[6]*x1 + diag[11]*x2  + diag[16]*x3 + diag[21]*x4;
      yy[ncnt+2] = diag[2]*x0 + diag[7]*x1 + diag[12]*x2 + diag[17]*x3 + diag[22]*x4;
      yy[ncnt+3] = diag[3]*x0 + diag[8]*x1 + diag[13]*x2 + diag[18]*x3 + diag[23]*x4;
      yy[ncnt+4] = diag[4]*x0 + diag[9]*x1 + diag[14]*x2 + diag[19]*x3 + diag[24]*x4;
      break;
    case 6:
      x0 = xx[ncnt]; x1 = xx[ncnt+1]; x2 = xx[ncnt+2]; x3 = xx[ncnt+3]; x4 = xx[ncnt+4]; x5 = xx[ncnt+5];
      yy[ncnt]   = diag[0]*x0 + diag[6]*x1  + diag[12]*x2  + diag[18]*x3 + diag[24]*x4 + diag[30]*x5;
      yy[ncnt+1] = diag[1]*x0 + diag[7]*x1  + diag[13]*x2  + diag[19]*x3 + diag[25]*x4 + diag[31]*x5;
      yy[ncnt+2] = diag[2]*x0 + diag[8]*x1  + diag[14]*x2  + diag[20]*x3 + diag[26]*x4 + diag[32]*x5;
      yy[ncnt+3] = diag[3]*x0 + diag[9]*x1  + diag[15]*x2  + diag[21]*x3 + diag[27]*x4 + diag[33]*x5;
      yy[ncnt+4] = diag[4]*x0 + diag[10]*x1 + diag[16]*x2  + diag[22]*x3 + diag[28]*x4 + diag[34]*x5;
      yy[ncnt+5] = diag[5]*x0 + diag[11]*x1 + diag[17]*x2  + diag[23]*x3 + diag[29]*x4 + diag[35]*x5;
      break;
    case 7:
      x0 = xx[ncnt]; x1 = xx[ncnt+1]; x2 = xx[ncnt+2]; x3 = xx[ncnt+3]; x4 = xx[ncnt+4]; x5 = xx[ncnt+5]; x6 = xx[ncnt+6];
      yy[ncnt]   = diag[0]*x0 + diag[7]*x1  + diag[14]*x2  + diag[21]*x3 + diag[28]*x4 + diag[35]*x5 + diag[42]*x6;
      yy[ncnt+1] = diag[1]*x0 + diag[8]*x1  + diag[15]*x2  + diag[22]*x3 + diag[29]*x4 + diag[36]*x5 + diag[43]*x6;
      yy[ncnt+2] = diag[2]*x0 + diag[9]*x1  + diag[16]*x2  + diag[23]*x3 + diag[30]*x4 + diag[37]*x5 + diag[44]*x6;
      yy[ncnt+3] = diag[3]*x0 + diag[10]*x1 + diag[17]*x2  + diag[24]*x3 + diag[31]*x4 + diag[38]*x5 + diag[45]*x6;
      yy[ncnt+4] = diag[4]*x0 + diag[11]*x1 + diag[18]*x2  + diag[25]*x3 + diag[32]*x4 + diag[39]*x5 + diag[46]*x6;
      yy[ncnt+5] = diag[5]*x0 + diag[12]*x1 + diag[19]*x2  + diag[26]*x3 + diag[33]*x4 + diag[40]*x5 + diag[47]*x6;
      yy[ncnt+6] = diag[6]*x0 + diag[13]*x1 + diag[20]*x2  + diag[27]*x3 + diag[34]*x4 + diag[41]*x5 + diag[48]*x6;
      break;
    default:
      for (ib=0; ib<bs; ib++) {
        PetscScalar rowsum = 0;
        for (jb=0; jb<bs; jb++) {
          rowsum += diag[ib+jb*bs] * xx[ncnt+jb];
        }
        yy[ncnt+ib] = rowsum;
      }
    }
    ncnt += bsizes[i];
    diag += bsizes[i]*bsizes[i];
  }
  PetscCall(VecRestoreArrayRead(x,&xx));
  PetscCall(VecRestoreArray(y,&yy));
  PetscFunctionReturn(0);
}

static PetscErrorCode PCSetUp_VPBJacobi(PC pc)
{
  PC_VPBJacobi    *jac = (PC_VPBJacobi*)pc->data;
  Mat            A = pc->pmat;
  MatFactorError err;
  PetscInt       i,nsize = 0,nlocal;
  PetscInt       nblocks;
  const PetscInt *bsizes;

  PetscFunctionBegin;
  PetscCall(MatGetVariableBlockSizes(pc->pmat,&nblocks,&bsizes));
  PetscCall(MatGetLocalSize(pc->pmat,&nlocal,NULL));
  PetscCheck(!nlocal || nblocks,PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"Must call MatSetVariableBlockSizes() before using PCVPBJACOBI");
  if (!jac->diag) {
    for (i=0; i<nblocks; i++) nsize += bsizes[i]*bsizes[i];
    PetscCall(PetscMalloc1(nsize,&jac->diag));
  }
  PetscCall(MatInvertVariableBlockDiagonal(A,nblocks,bsizes,jac->diag));
  PetscCall(MatFactorGetError(A,&err));
  if (err) pc->failedreason = (PCFailedReason)err;
  pc->ops->apply = PCApply_VPBJacobi;
  PetscFunctionReturn(0);
}

static PetscErrorCode PCDestroy_VPBJacobi(PC pc)
{
  PC_VPBJacobi    *jac = (PC_VPBJacobi*)pc->data;

  PetscFunctionBegin;
  /*
      Free the private data structure that was hanging off the PC
  */
  PetscCall(PetscFree(jac->diag));
  PetscCall(PetscFree(pc->data));
  PetscFunctionReturn(0);
}

/*MC
     PCVPBJACOBI - Variable size point block Jacobi preconditioner

   Notes:
     See PCJACOBI for point Jacobi preconditioning, PCPBJACOBI for fixed point block size, and PCBJACOBI for large size blocks

     This works for AIJ matrices

     Uses dense LU factorization with partial pivoting to invert the blocks; if a zero pivot
     is detected a PETSc error is generated.

     One must call MatSetVariableBlockSizes() to use this preconditioner

   Developer Notes:
     This should support the PCSetErrorIfFailure() flag set to PETSC_TRUE to allow
     the factorization to continue even after a zero pivot is found resulting in a Nan and hence
     terminating KSP with a KSP_DIVERGED_NANORIF allowing
     a nonlinear solver/ODE integrator to recover without stopping the program as currently happens.

     Perhaps should provide an option that allows generation of a valid preconditioner
     even if a block is singular as the PCJACOBI does.

   Level: beginner

.seealso:  MatSetVariableBlockSizes(), PCCreate(), PCSetType(), PCType (for list of available types), PC, PCJACOBI, PCPBJACOBI, PCBJACOBI

M*/

PETSC_EXTERN PetscErrorCode PCCreate_VPBJacobi(PC pc)
{
  PC_VPBJacobi   *jac;

  PetscFunctionBegin;
  /*
     Creates the private data structure for this preconditioner and
     attach it to the PC object.
  */
  PetscCall(PetscNewLog(pc,&jac));
  pc->data = (void*)jac;

  /*
     Initialize the pointers to vectors to ZERO; these will be used to store
     diagonal entries of the matrix for fast preconditioner application.
  */
  jac->diag = NULL;

  /*
      Set the pointers for the functions that are provided above.
      Now when the user-level routines (such as PCApply(), PCDestroy(), etc.)
      are called, they will automatically call these functions.  Note we
      choose not to provide a couple of these functions since they are
      not needed.
  */
  pc->ops->apply               = PCApply_VPBJacobi;
  pc->ops->applytranspose      = NULL;
  pc->ops->setup               = PCSetUp_VPBJacobi;
  pc->ops->destroy             = PCDestroy_VPBJacobi;
  pc->ops->setfromoptions      = NULL;
  pc->ops->applyrichardson     = NULL;
  pc->ops->applysymmetricleft  = NULL;
  pc->ops->applysymmetricright = NULL;
  PetscFunctionReturn(0);
}