xref: /petsc/src/mat/impls/aij/seq/symtranspose.c (revision 7fb60732ccf1806988e9909cd147cdb09c395756)

/*
  Defines transpose routines for SeqAIJ matrices.
*/

#include <../src/mat/impls/aij/seq/aij.h>

/*
   The symbolic and full transpose versions share several similar code blocks but the macros to reuse the code would be confusing and ugly
*/
PetscErrorCode MatTransposeSymbolic_SeqAIJ(Mat A,Mat *B)
{
  PetscInt       i,j,anzj;
  Mat            At;
  Mat_SeqAIJ     *a=(Mat_SeqAIJ*)A->data,*at;
  PetscInt       an=A->cmap->N,am=A->rmap->N;
  PetscInt       *ati,*atj,*atfill,*ai=a->i,*aj=a->j;

  PetscFunctionBegin;
  /* Allocate space for symbolic transpose info and work array */
  PetscCall(PetscCalloc1(an+1,&ati));
  PetscCall(PetscMalloc1(ai[am],&atj));

  /* Walk through aj and count ## of non-zeros in each row of A^T. */
  /* Note: offset by 1 for fast conversion into csr format. */
  for (i=0;i<ai[am];i++) ati[aj[i]+1] += 1;
  /* Form ati for csr format of A^T. */
  for (i=0;i<an;i++) ati[i+1] += ati[i];

  /* Copy ati into atfill so we have locations of the next free space in atj */
  PetscCall(PetscMalloc1(an,&atfill));
  PetscCall(PetscArraycpy(atfill,ati,an));

  /* Walk through A row-wise and mark nonzero entries of A^T. */
  for (i=0;i<am;i++) {
    anzj = ai[i+1] - ai[i];
    for (j=0;j<anzj;j++) {
      atj[atfill[*aj]] = i;
      atfill[*aj++]   += 1;
    }
  }
  PetscCall(PetscFree(atfill));

  PetscCall(MatCreateSeqAIJWithArrays(PetscObjectComm((PetscObject)A),an,am,ati,atj,NULL,&At));
  PetscCall(MatSetBlockSizes(At,PetscAbs(A->cmap->bs),PetscAbs(A->rmap->bs)));
  PetscCall(MatSetType(At,((PetscObject)A)->type_name));
  at          = (Mat_SeqAIJ*)At->data;
  at->free_a  = PETSC_FALSE;
  at->free_ij = PETSC_TRUE;
  at->nonew   = 0;
  at->maxnz   = ati[an];
  *B = At;
  PetscFunctionReturn(0);
}

PetscErrorCode MatTranspose_SeqAIJ(Mat A,MatReuse reuse,Mat *B)
{
  PetscInt        i,j,anzj;
  Mat             At;
  Mat_SeqAIJ      *a=(Mat_SeqAIJ*)A->data,*at;
  PetscInt        an=A->cmap->N,am=A->rmap->N;
  PetscInt        *ati,*atj,*atfill,*ai=a->i,*aj=a->j;
  MatScalar       *ata;
  const MatScalar *aa,*av;
  PetscContainer  rB;
  MatParentState  *rb;
  PetscBool       nonzerochange = PETSC_FALSE;

  PetscFunctionBegin;
  if (reuse == MAT_REUSE_MATRIX) {
    PetscCall(PetscObjectQuery((PetscObject)*B,"MatTransposeParent",(PetscObject*)&rB));
    PetscCheck(rB,PetscObjectComm((PetscObject)*B),PETSC_ERR_ARG_WRONG,"Reuse matrix used was not generated from call to MatTranspose()");
    PetscCall(PetscContainerGetPointer(rB,(void**)&rb));
    if (rb->nonzerostate != A->nonzerostate) nonzerochange = PETSC_TRUE;
  }

  PetscCall(MatSeqAIJGetArrayRead(A,&av));
  aa   = av;
  if (reuse == MAT_INITIAL_MATRIX || reuse == MAT_INPLACE_MATRIX || nonzerochange) {
    /* Allocate space for symbolic transpose info and work array */
    PetscCall(PetscCalloc1(an+1,&ati));
    PetscCall(PetscMalloc1(ai[am],&atj));
    /* Walk through aj and count ## of non-zeros in each row of A^T. */
    /* Note: offset by 1 for fast conversion into csr format. */
    for (i=0;i<ai[am];i++) ati[aj[i]+1] += 1;
    /* Form ati for csr format of A^T. */
    for (i=0;i<an;i++) ati[i+1] += ati[i];
    PetscCall(PetscMalloc1(ai[am],&ata));
  } else {
    Mat_SeqAIJ *sub_B = (Mat_SeqAIJ*) (*B)->data;
    ati = sub_B->i;
    atj = sub_B->j;
    ata = sub_B->a;
    At  = *B;
  }

  /* Copy ati into atfill so we have locations of the next free space in atj */
  PetscCall(PetscMalloc1(an,&atfill));
  PetscCall(PetscArraycpy(atfill,ati,an));

  /* Walk through A row-wise and mark nonzero entries of A^T. */
  for (i=0;i<am;i++) {
    anzj = ai[i+1] - ai[i];
    for (j=0;j<anzj;j++) {
      atj[atfill[*aj]] = i;
      ata[atfill[*aj]] = *aa++;
      atfill[*aj++]   += 1;
    }
  }
  PetscCall(PetscFree(atfill));
  PetscCall(MatSeqAIJRestoreArrayRead(A,&av));
  if (reuse == MAT_REUSE_MATRIX) PetscCall(PetscObjectStateIncrease((PetscObject)(*B)));

  if (reuse == MAT_INITIAL_MATRIX || reuse == MAT_INPLACE_MATRIX || nonzerochange) {
    PetscCall(MatCreateSeqAIJWithArrays(PetscObjectComm((PetscObject)A),an,am,ati,atj,ata,&At));
    PetscCall(MatSetBlockSizes(At,PetscAbs(A->cmap->bs),PetscAbs(A->rmap->bs)));
    PetscCall(MatSetType(At,((PetscObject)A)->type_name));
    at          = (Mat_SeqAIJ*)(At->data);
    at->free_a  = PETSC_TRUE;
    at->free_ij = PETSC_TRUE;
    at->nonew   = 0;
    at->maxnz   = ati[an];
  }

  if (reuse == MAT_INITIAL_MATRIX || (reuse == MAT_REUSE_MATRIX && !nonzerochange)) {
    *B = At;
  } else if (nonzerochange) {
    PetscCall(MatHeaderMerge(*B,&At));
    PetscCall(MatTransposeSetPrecursor(A,*B));
  } else if (reuse == MAT_INPLACE_MATRIX) {
    PetscCall(MatHeaderMerge(A,&At));
  }
  PetscFunctionReturn(0);
}

/*
   Get symbolic matrix structure of a submatrix of A, A[rstart:rend,:],
*/
PetscErrorCode MatGetSymbolicTransposeReduced_SeqAIJ(Mat A,PetscInt rstart,PetscInt rend,PetscInt *Ati[],PetscInt *Atj[])
{
  PetscInt       i,j,anzj;
  Mat_SeqAIJ     *a=(Mat_SeqAIJ*)A->data;
  PetscInt       an=A->cmap->N;
  PetscInt       *ati,*atj,*atfill,*ai=a->i,*aj=a->j, am=ai[rend] - ai[rstart];

  PetscFunctionBegin;
  PetscCall(PetscLogEventBegin(MAT_Getsymtransreduced,A,0,0,0));

  /* Allocate space for symbolic transpose info and work array */
  PetscCall(PetscCalloc1(an+1,&ati));
  PetscCall(PetscMalloc1(am+1,&atj));

  /* Walk through aj and count ## of non-zeros in each row of A^T. */
  /* Note: offset by 1 for fast conversion into csr format. */
  for (i=ai[rstart]; i<ai[rend]; i++) ati[aj[i]+1] += 1;
  /* Form ati for csr format of A^T. */
  for (i=0;i<an;i++) ati[i+1] += ati[i];

  /* Copy ati into atfill so we have locations of the next free space in atj */
  PetscCall(PetscMalloc1(an+1,&atfill));
  PetscCall(PetscArraycpy(atfill,ati,an));

  /* Walk through A row-wise and mark nonzero entries of A^T. */
  aj = aj + ai[rstart];
  for (i=rstart; i<rend; i++) {
    anzj = ai[i+1] - ai[i];
    for (j=0; j<anzj; j++) {
      atj[atfill[*aj]] = i-rstart;
      atfill[*aj++]   += 1;
    }
  }
  PetscCall(PetscFree(atfill));
  *Ati = ati;
  *Atj = atj;

  PetscCall(PetscLogEventEnd(MAT_Getsymtransreduced,A,0,0,0));
  PetscFunctionReturn(0);
}

/*
    Returns the i and j arrays for a symbolic transpose, this is used internally within SeqAIJ code when the full
    symbolic matrix (which can be obtained with MatTransposeSymbolic() is not needed. MatRestoreSymbolicTranspose_SeqAIJ() should be used to free the arrays.
*/
PetscErrorCode MatGetSymbolicTranspose_SeqAIJ(Mat A,PetscInt *Ati[],PetscInt *Atj[])
{
  PetscFunctionBegin;
  PetscCall(MatGetSymbolicTransposeReduced_SeqAIJ(A,0,A->rmap->N,Ati,Atj));
  PetscFunctionReturn(0);
}

PetscErrorCode MatRestoreSymbolicTranspose_SeqAIJ(Mat A,PetscInt *ati[],PetscInt *atj[])
{
  PetscFunctionBegin;
  PetscCall(PetscFree(*ati));
  PetscCall(PetscFree(*atj));
  PetscFunctionReturn(0);
}