xref: /petsc/src/ksp/pc/impls/fieldsplit/fieldsplit.c (revision d32f9abdbc052d6e1fd06679b17a55415c3aae30)

#define PETSCKSP_DLL

/*

*/
#include "private/pcimpl.h"     /*I "petscpc.h" I*/

typedef struct _PC_FieldSplitLink *PC_FieldSplitLink;
struct _PC_FieldSplitLink {
  KSP               ksp;
  Vec               x,y;
  PetscInt          nfields;
  PetscInt          *fields;
  VecScatter        sctx;
  IS                is,cis;
  PetscInt          csize;
  PC_FieldSplitLink next,previous;
};

typedef struct {
  PCCompositeType   type;              /* additive or multiplicative */
  PetscTruth        defaultsplit;
  PetscInt          bs;
  PetscInt          nsplits;
  Vec               *x,*y,w1,w2;
  Mat               *pmat;
  PetscTruth        issetup;
  PC_FieldSplitLink head;
} PC_FieldSplit;

/*
    Notes: there is no particular reason that pmat, x, and y are stored as arrays in PC_FieldSplit instead of
   inside PC_FieldSplitLink, just historical. If you want to be able to add new fields after already using the
   PC you could change this.
*/
#undef __FUNCT__
#define __FUNCT__ "PCView_FieldSplit"
static PetscErrorCode PCView_FieldSplit(PC pc,PetscViewer viewer)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PetscTruth        iascii;
  PetscInt          i,j;
  PC_FieldSplitLink ilink = jac->head;

  PetscFunctionBegin;
  ierr = PetscTypeCompare((PetscObject)viewer,PETSC_VIEWER_ASCII,&iascii);CHKERRQ(ierr);
  if (iascii) {
    ierr = PetscViewerASCIIPrintf(viewer,"  FieldSplit with %s composition: total splits = %D, blocksize = %D\n",PCCompositeTypes[jac->type],jac->nsplits,jac->bs);CHKERRQ(ierr);
    ierr = PetscViewerASCIIPrintf(viewer,"  Solver info for each split is in the following KSP objects:\n");CHKERRQ(ierr);
    ierr = PetscViewerASCIIPushTab(viewer);CHKERRQ(ierr);
    for (i=0; i<jac->nsplits; i++) {
      if (ilink->fields) {
	ierr = PetscViewerASCIIPrintf(viewer,"Split number %D Fields ",i);CHKERRQ(ierr);
	ierr = PetscViewerASCIIUseTabs(viewer,PETSC_FALSE);CHKERRQ(ierr);
	for (j=0; j<ilink->nfields; j++) {
	  if (j > 0) {
	    ierr = PetscViewerASCIIPrintf(viewer,",");CHKERRQ(ierr);
	  }
	  ierr = PetscViewerASCIIPrintf(viewer," %D",ilink->fields[j]);CHKERRQ(ierr);
	}
	ierr = PetscViewerASCIIPrintf(viewer,"\n");CHKERRQ(ierr);
        ierr = PetscViewerASCIIUseTabs(viewer,PETSC_TRUE);CHKERRQ(ierr);
      } else {
	ierr = PetscViewerASCIIPrintf(viewer,"Split number %D Defined by IS\n",i);CHKERRQ(ierr);
      }
      ierr = KSPView(ilink->ksp,viewer);CHKERRQ(ierr);
      ilink = ilink->next;
    }
    ierr = PetscViewerASCIIPopTab(viewer);CHKERRQ(ierr);
  } else {
    SETERRQ1(PETSC_ERR_SUP,"Viewer type %s not supported for PCFieldSplit",((PetscObject)viewer)->type_name);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetDefaults"
static PetscErrorCode PCFieldSplitSetDefaults(PC pc)
{
  PC_FieldSplit     *jac  = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink = jac->head;
  PetscInt          i = 0,*ifields,nfields;
  PetscTruth        flg = PETSC_FALSE,*fields,flg2;
  char              optionname[128];

  PetscFunctionBegin;
  if (!ilink) {

    if (jac->bs <= 0) {
      if (pc->pmat) {
        ierr   = MatGetBlockSize(pc->pmat,&jac->bs);CHKERRQ(ierr);
      } else {
        jac->bs = 1;
      }
    }

    ierr = PetscOptionsGetTruth(((PetscObject)pc)->prefix,"-pc_fieldsplit_default",&flg,PETSC_NULL);CHKERRQ(ierr);
    if (!flg) {
      /* Allow user to set fields from command line,  if bs was known at the time of PCSetFromOptions_FieldSplit()
         then it is set there. This is not ideal because we should only have options set in XXSetFromOptions(). */
      flg = PETSC_TRUE; /* switched off automatically if user sets fields manually here */
      ierr = PetscMalloc(jac->bs*sizeof(PetscInt),&ifields);CHKERRQ(ierr);
      while (PETSC_TRUE) {
        sprintf(optionname,"-pc_fieldsplit_%d_fields",(int)i++);
        nfields = jac->bs;
        ierr    = PetscOptionsGetIntArray(((PetscObject)pc)->prefix,optionname,ifields,&nfields,&flg2);CHKERRQ(ierr);
        if (!flg2) break;
        if (!nfields) SETERRQ(PETSC_ERR_USER,"Cannot list zero fields");
        flg = PETSC_FALSE;
        ierr = PCFieldSplitSetFields(pc,nfields,ifields);CHKERRQ(ierr);
      }
      ierr = PetscFree(ifields);CHKERRQ(ierr);
    }

    if (flg) {
      ierr = PetscInfo(pc,"Using default splitting of fields\n");CHKERRQ(ierr);
      ierr = PetscMalloc(jac->bs*sizeof(PetscTruth),&fields);CHKERRQ(ierr);
      ierr = PetscMemzero(fields,jac->bs*sizeof(PetscTruth));CHKERRQ(ierr);
      while (ilink) {
	for (i=0; i<ilink->nfields; i++) {
	  fields[ilink->fields[i]] = PETSC_TRUE;
	}
	ilink = ilink->next;
      }
      jac->defaultsplit = PETSC_TRUE;
      for (i=0; i<jac->bs; i++) {
	if (!fields[i]) {
	  ierr = PCFieldSplitSetFields(pc,1,&i);CHKERRQ(ierr);
	} else {
	  jac->defaultsplit = PETSC_FALSE;
	}
      }
    }
  }
  PetscFunctionReturn(0);
}


#undef __FUNCT__
#define __FUNCT__ "PCSetUp_FieldSplit"
static PetscErrorCode PCSetUp_FieldSplit(PC pc)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink;
  PetscInt          i,nsplit,ccsize;
  MatStructure      flag = pc->flag;
  PetscTruth        sorted;

  PetscFunctionBegin;
  ierr   = PCFieldSplitSetDefaults(pc);CHKERRQ(ierr);
  nsplit = jac->nsplits;
  ilink  = jac->head;

  /* get the matrices for each split */
  if (!jac->issetup) {
    PetscInt rstart,rend,nslots,bs;

    jac->issetup = PETSC_TRUE;

    /* This is done here instead of in PCFieldSplitSetFields() because may not have matrix at that point */
    bs     = jac->bs;
    ierr   = MatGetOwnershipRange(pc->pmat,&rstart,&rend);CHKERRQ(ierr);
    ierr   = MatGetLocalSize(pc->pmat,PETSC_NULL,&ccsize);CHKERRQ(ierr);
    nslots = (rend - rstart)/bs;
    for (i=0; i<nsplit; i++) {
      if (jac->defaultsplit) {
        ierr = ISCreateStride(((PetscObject)pc)->comm,nslots,rstart+i,nsplit,&ilink->is);CHKERRQ(ierr);
        ilink->csize = ccsize/nsplit;
      } else if (!ilink->is) {
        if (ilink->nfields > 1) {
          PetscInt   *ii,j,k,nfields = ilink->nfields,*fields = ilink->fields;
          ierr = PetscMalloc(ilink->nfields*nslots*sizeof(PetscInt),&ii);CHKERRQ(ierr);
          for (j=0; j<nslots; j++) {
            for (k=0; k<nfields; k++) {
              ii[nfields*j + k] = rstart + bs*j + fields[k];
            }
          }
          ierr = ISCreateGeneral(((PetscObject)pc)->comm,nslots*nfields,ii,&ilink->is);CHKERRQ(ierr);
          ierr = PetscFree(ii);CHKERRQ(ierr);
        } else {
          ierr = ISCreateStride(((PetscObject)pc)->comm,nslots,rstart+ilink->fields[0],bs,&ilink->is);CHKERRQ(ierr);
        }
        ilink->csize = (ccsize/bs)*ilink->nfields;
        ierr = ISSorted(ilink->is,&sorted);CHKERRQ(ierr);
        if (!sorted) SETERRQ(PETSC_ERR_USER,"Fields must be sorted when creating split");
      }
      ierr  = ISAllGather(ilink->is,&ilink->cis);CHKERRQ(ierr);
      ilink = ilink->next;
    }
  }

  ilink  = jac->head;
  if (!jac->pmat) {
    ierr = PetscMalloc(nsplit*sizeof(Mat),&jac->pmat);CHKERRQ(ierr);
    for (i=0; i<nsplit; i++) {
      ierr = MatGetSubMatrix(pc->pmat,ilink->is,ilink->cis,ilink->csize,MAT_INITIAL_MATRIX,&jac->pmat[i]);CHKERRQ(ierr);
      ilink = ilink->next;
    }
  } else {
    for (i=0; i<nsplit; i++) {
      ierr = MatGetSubMatrix(pc->pmat,ilink->is,ilink->cis,ilink->csize,MAT_REUSE_MATRIX,&jac->pmat[i]);CHKERRQ(ierr);
      ilink = ilink->next;
    }
  }

  /* set up the individual PCs */
  i    = 0;
  ilink = jac->head;
  while (ilink) {
    ierr = KSPSetOperators(ilink->ksp,jac->pmat[i],jac->pmat[i],flag);CHKERRQ(ierr);
    ierr = KSPSetFromOptions(ilink->ksp);CHKERRQ(ierr);
    ierr = KSPSetUp(ilink->ksp);CHKERRQ(ierr);
    i++;
    ilink = ilink->next;
  }

  /* create work vectors for each split */
  if (!jac->x) {
    Vec xtmp;
    ierr = PetscMalloc2(nsplit,Vec,&jac->x,nsplit,Vec,&jac->y);CHKERRQ(ierr);
    ilink = jac->head;
    for (i=0; i<nsplit; i++) {
      Vec *vl,*vr;

      ierr      = KSPGetVecs(ilink->ksp,1,&vr,1,&vl);CHKERRQ(ierr);
      ilink->x  = *vr;
      ilink->y  = *vl;
      ierr      = PetscFree(vr);CHKERRQ(ierr);
      ierr      = PetscFree(vl);CHKERRQ(ierr);
      jac->x[i] = ilink->x;
      jac->y[i] = ilink->y;
      ilink     = ilink->next;
    }
    /* compute scatter contexts needed by multiplicative versions and non-default splits */

    ilink = jac->head;
    ierr = MatGetVecs(pc->pmat,&xtmp,PETSC_NULL);CHKERRQ(ierr);
    for (i=0; i<nsplit; i++) {
      ierr = VecScatterCreate(xtmp,ilink->is,jac->x[i],PETSC_NULL,&ilink->sctx);CHKERRQ(ierr);
      ilink = ilink->next;
    }
    ierr = VecDestroy(xtmp);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#define FieldSplitSplitSolveAdd(ilink,xx,yy) \
    (VecScatterBegin(ilink->sctx,xx,ilink->x,INSERT_VALUES,SCATTER_FORWARD) || \
     VecScatterEnd(ilink->sctx,xx,ilink->x,INSERT_VALUES,SCATTER_FORWARD) || \
     KSPSolve(ilink->ksp,ilink->x,ilink->y) || \
     VecScatterBegin(ilink->sctx,ilink->y,yy,ADD_VALUES,SCATTER_REVERSE) || \
     VecScatterEnd(ilink->sctx,ilink->y,yy,ADD_VALUES,SCATTER_REVERSE))

#undef __FUNCT__
#define __FUNCT__ "PCApply_FieldSplit"
static PetscErrorCode PCApply_FieldSplit(PC pc,Vec x,Vec y)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink = jac->head;
  PetscInt          bs;

  PetscFunctionBegin;
  CHKMEMQ;
  ierr = VecGetBlockSize(x,&bs);CHKERRQ(ierr);
  ierr = VecSetBlockSize(x,jac->bs);CHKERRQ(ierr);
  ierr = VecSetBlockSize(y,jac->bs);CHKERRQ(ierr);

  if (jac->type == PC_COMPOSITE_ADDITIVE) {
    if (jac->defaultsplit) {
      ierr = VecStrideGatherAll(x,jac->x,INSERT_VALUES);CHKERRQ(ierr);
      while (ilink) {
        ierr = KSPSolve(ilink->ksp,ilink->x,ilink->y);CHKERRQ(ierr);
        ilink = ilink->next;
      }
      ierr = VecStrideScatterAll(jac->y,y,INSERT_VALUES);CHKERRQ(ierr);
    } else {
      ierr = VecSet(y,0.0);CHKERRQ(ierr);
      while (ilink) {
        ierr = FieldSplitSplitSolveAdd(ilink,x,y);CHKERRQ(ierr);
        ilink = ilink->next;
      }
    }
  } else if (jac->type == PC_COMPOSITE_MULTIPLICATIVE || jac->type == PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE) {
    if (!jac->w1) {
      ierr = VecDuplicate(x,&jac->w1);CHKERRQ(ierr);
      ierr = VecDuplicate(x,&jac->w2);CHKERRQ(ierr);
    }
    ierr = VecSet(y,0.0);CHKERRQ(ierr);
    ierr = FieldSplitSplitSolveAdd(ilink,x,y);CHKERRQ(ierr);
    while (ilink->next) {
      ilink = ilink->next;
      ierr  = MatMult(pc->mat,y,jac->w1);CHKERRQ(ierr);
      ierr  = VecWAXPY(jac->w2,-1.0,jac->w1,x);CHKERRQ(ierr);
      ierr  = FieldSplitSplitSolveAdd(ilink,jac->w2,y);CHKERRQ(ierr);
    }
    if (jac->type == PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE) {
      while (ilink->previous) {
        ilink = ilink->previous;
        ierr  = MatMult(pc->mat,y,jac->w1);CHKERRQ(ierr);
        ierr  = VecWAXPY(jac->w2,-1.0,jac->w1,x);CHKERRQ(ierr);
        ierr  = FieldSplitSplitSolveAdd(ilink,jac->w2,y);CHKERRQ(ierr);
      }
    }
  } else SETERRQ1(PETSC_ERR_SUP,"Unsupported or unknown composition",(int) jac->type);
  CHKMEMQ;
  PetscFunctionReturn(0);
}

#define FieldSplitSplitSolveAddTranspose(ilink,xx,yy) \
    (VecScatterBegin(ilink->sctx,xx,ilink->y,INSERT_VALUES,SCATTER_FORWARD) || \
     VecScatterEnd(ilink->sctx,xx,ilink->y,INSERT_VALUES,SCATTER_FORWARD) || \
     KSPSolveTranspose(ilink->ksp,ilink->y,ilink->x) || \
     VecScatterBegin(ilink->sctx,ilink->x,yy,ADD_VALUES,SCATTER_REVERSE) || \
     VecScatterEnd(ilink->sctx,ilink->x,yy,ADD_VALUES,SCATTER_REVERSE))

#undef __FUNCT__
#define __FUNCT__ "PCApply_FieldSplit"
static PetscErrorCode PCApplyTranspose_FieldSplit(PC pc,Vec x,Vec y)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink = jac->head;
  PetscInt          bs;

  PetscFunctionBegin;
  CHKMEMQ;
  ierr = VecGetBlockSize(x,&bs);CHKERRQ(ierr);
  ierr = VecSetBlockSize(x,jac->bs);CHKERRQ(ierr);
  ierr = VecSetBlockSize(y,jac->bs);CHKERRQ(ierr);

  if (jac->type == PC_COMPOSITE_ADDITIVE) {
    if (jac->defaultsplit) {
      ierr = VecStrideGatherAll(x,jac->x,INSERT_VALUES);CHKERRQ(ierr);
      while (ilink) {
	ierr = KSPSolveTranspose(ilink->ksp,ilink->x,ilink->y);CHKERRQ(ierr);
	ilink = ilink->next;
      }
      ierr = VecStrideScatterAll(jac->y,y,INSERT_VALUES);CHKERRQ(ierr);
    } else {
      ierr = VecSet(y,0.0);CHKERRQ(ierr);
      while (ilink) {
        ierr = FieldSplitSplitSolveAddTranspose(ilink,x,y);CHKERRQ(ierr);
	ilink = ilink->next;
      }
    }
  } else {
    if (!jac->w1) {
      ierr = VecDuplicate(x,&jac->w1);CHKERRQ(ierr);
      ierr = VecDuplicate(x,&jac->w2);CHKERRQ(ierr);
    }
    ierr = VecSet(y,0.0);CHKERRQ(ierr);
    if (jac->type == PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE) {
      ierr = FieldSplitSplitSolveAddTranspose(ilink,x,y);CHKERRQ(ierr);
      while (ilink->next) {
        ilink = ilink->next;
        ierr  = MatMultTranspose(pc->mat,y,jac->w1);CHKERRQ(ierr);
        ierr  = VecWAXPY(jac->w2,-1.0,jac->w1,x);CHKERRQ(ierr);
        ierr  = FieldSplitSplitSolveAddTranspose(ilink,jac->w2,y);CHKERRQ(ierr);
      }
      while (ilink->previous) {
        ilink = ilink->previous;
        ierr  = MatMultTranspose(pc->mat,y,jac->w1);CHKERRQ(ierr);
        ierr  = VecWAXPY(jac->w2,-1.0,jac->w1,x);CHKERRQ(ierr);
        ierr  = FieldSplitSplitSolveAddTranspose(ilink,jac->w2,y);CHKERRQ(ierr);
      }
    } else {
      while (ilink->next) {   /* get to last entry in linked list */
	ilink = ilink->next;
      }
      ierr = FieldSplitSplitSolveAddTranspose(ilink,x,y);CHKERRQ(ierr);
      while (ilink->previous) {
	ilink = ilink->previous;
	ierr  = MatMultTranspose(pc->mat,y,jac->w1);CHKERRQ(ierr);
	ierr  = VecWAXPY(jac->w2,-1.0,jac->w1,x);CHKERRQ(ierr);
	ierr  = FieldSplitSplitSolveAddTranspose(ilink,jac->w2,y);CHKERRQ(ierr);
      }
    }
  }
  CHKMEMQ;
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCDestroy_FieldSplit"
static PetscErrorCode PCDestroy_FieldSplit(PC pc)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink = jac->head,next;

  PetscFunctionBegin;
  while (ilink) {
    ierr = KSPDestroy(ilink->ksp);CHKERRQ(ierr);
    if (ilink->x) {ierr = VecDestroy(ilink->x);CHKERRQ(ierr);}
    if (ilink->y) {ierr = VecDestroy(ilink->y);CHKERRQ(ierr);}
    if (ilink->sctx) {ierr = VecScatterDestroy(ilink->sctx);CHKERRQ(ierr);}
    if (ilink->is) {ierr = ISDestroy(ilink->is);CHKERRQ(ierr);}
    if (ilink->cis) {ierr = ISDestroy(ilink->cis);CHKERRQ(ierr);}
    next = ilink->next;
    ierr = PetscFree(ilink->fields);CHKERRQ(ierr);
    ierr = PetscFree(ilink);CHKERRQ(ierr);
    ilink = next;
  }
  ierr = PetscFree2(jac->x,jac->y);CHKERRQ(ierr);
  if (jac->pmat) {ierr = MatDestroyMatrices(jac->nsplits,&jac->pmat);CHKERRQ(ierr);}
  if (jac->w1) {ierr = VecDestroy(jac->w1);CHKERRQ(ierr);}
  if (jac->w2) {ierr = VecDestroy(jac->w2);CHKERRQ(ierr);}
  ierr = PetscFree(jac);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCSetFromOptions_FieldSplit"
static PetscErrorCode PCSetFromOptions_FieldSplit(PC pc)
{
  PetscErrorCode ierr;
  PetscInt       i = 0,nfields,*fields,bs;
  PetscTruth     flg;
  char           optionname[128];
  PC_FieldSplit  *jac = (PC_FieldSplit*)pc->data;

  PetscFunctionBegin;
  ierr = PetscOptionsHead("FieldSplit options");CHKERRQ(ierr);
  ierr = PetscOptionsInt("-pc_fieldsplit_block_size","Blocksize that defines number of fields","PCFieldSplitSetBlockSize",jac->bs,&bs,&flg);CHKERRQ(ierr);
  if (flg) {
    ierr = PCFieldSplitSetBlockSize(pc,bs);CHKERRQ(ierr);
  }

  ierr = PetscOptionsEnum("-pc_fieldsplit_type","Type of composition","PCFieldSplitSetType",PCCompositeTypes,(PetscEnum)jac->type,(PetscEnum*)&jac->type,&flg);CHKERRQ(ierr);

  if (jac->bs > 0) {
    /* only allow user to set fields from command line if bs is already known.
       otherwise user can set them in PCFieldSplitSetDefaults() */
    ierr = PetscMalloc(jac->bs*sizeof(PetscInt),&fields);CHKERRQ(ierr);
    while (PETSC_TRUE) {
      sprintf(optionname,"-pc_fieldsplit_%d_fields",(int)i++);
      nfields = jac->bs;
      ierr    = PetscOptionsIntArray(optionname,"Fields in this split","PCFieldSplitSetFields",fields,&nfields,&flg);CHKERRQ(ierr);
      if (!flg) break;
      if (!nfields) SETERRQ(PETSC_ERR_USER,"Cannot list zero fields");
      ierr = PCFieldSplitSetFields(pc,nfields,fields);CHKERRQ(ierr);
    }
    ierr = PetscFree(fields);CHKERRQ(ierr);
  }
  ierr = PetscOptionsTail();CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

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

EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetFields_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetFields_FieldSplit(PC pc,PetscInt n,PetscInt *fields)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PC_FieldSplitLink ilink,next = jac->head;
  char              prefix[128];
  PetscInt          i;

  PetscFunctionBegin;
  if (n <= 0) SETERRQ(PETSC_ERR_ARG_OUTOFRANGE,"Negative number of fields requested");
  for (i=0; i<n; i++) {
    if (fields[i] >= jac->bs) SETERRQ2(PETSC_ERR_ARG_OUTOFRANGE,"Field %D requested but only %D exist",fields[i],jac->bs);
    if (fields[i] < 0) SETERRQ1(PETSC_ERR_ARG_OUTOFRANGE,"Negative field %D requested",fields[i]);
  }
  ierr = PetscNew(struct _PC_FieldSplitLink,&ilink);CHKERRQ(ierr);
  ierr = PetscMalloc(n*sizeof(PetscInt),&ilink->fields);CHKERRQ(ierr);
  ierr = PetscMemcpy(ilink->fields,fields,n*sizeof(PetscInt));CHKERRQ(ierr);
  ilink->nfields = n;
  ilink->next    = PETSC_NULL;
  ierr           = KSPCreate(((PetscObject)pc)->comm,&ilink->ksp);CHKERRQ(ierr);
  ierr           = KSPSetType(ilink->ksp,KSPPREONLY);CHKERRQ(ierr);

  if (((PetscObject)pc)->prefix) {
    sprintf(prefix,"%sfieldsplit_%d_",((PetscObject)pc)->prefix,(int)jac->nsplits);
  } else {
    sprintf(prefix,"fieldsplit_%d_",(int)jac->nsplits);
  }
  ierr = KSPSetOptionsPrefix(ilink->ksp,prefix);CHKERRQ(ierr);

  if (!next) {
    jac->head       = ilink;
    ilink->previous = PETSC_NULL;
  } else {
    while (next->next) {
      next = next->next;
    }
    next->next      = ilink;
    ilink->previous = next;
  }
  jac->nsplits++;
  PetscFunctionReturn(0);
}
EXTERN_C_END


EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitGetSubKSP_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitGetSubKSP_FieldSplit(PC pc,PetscInt *n,KSP **subksp)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
  PetscInt          cnt = 0;
  PC_FieldSplitLink ilink = jac->head;

  PetscFunctionBegin;
  ierr = PetscMalloc(jac->nsplits*sizeof(KSP*),subksp);CHKERRQ(ierr);
  while (ilink) {
    (*subksp)[cnt++] = ilink->ksp;
    ilink = ilink->next;
  }
  if (cnt != jac->nsplits) SETERRQ2(PETSC_ERR_PLIB,"Corrupt PCFIELDSPLIT object: number splits in linked list %D in object %D",cnt,jac->nsplits);
  *n = jac->nsplits;
  PetscFunctionReturn(0);
}
EXTERN_C_END

EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetIS_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetIS_FieldSplit(PC pc,IS is)
{
  PC_FieldSplit     *jac = (PC_FieldSplit*)pc->data;
  PetscErrorCode    ierr;
    PC_FieldSplitLink ilink, next = jac->head;
  char              prefix[128];

  PetscFunctionBegin;
  ierr = PetscNew(struct _PC_FieldSplitLink,&ilink);CHKERRQ(ierr);
  ilink->is      = is;
  ierr           = PetscObjectReference((PetscObject)is);CHKERRQ(ierr);
  ilink->next    = PETSC_NULL;
  ierr           = KSPCreate(((PetscObject)pc)->comm,&ilink->ksp);CHKERRQ(ierr);
  ierr           = KSPSetType(ilink->ksp,KSPPREONLY);CHKERRQ(ierr);

  if (((PetscObject)pc)->prefix) {
    sprintf(prefix,"%sfieldsplit_%d_",((PetscObject)pc)->prefix,(int)jac->nsplits);
  } else {
    sprintf(prefix,"fieldsplit_%d_",(int)jac->nsplits);
  }
  ierr = KSPSetOptionsPrefix(ilink->ksp,prefix);CHKERRQ(ierr);

  if (!next) {
    jac->head       = ilink;
    ilink->previous = PETSC_NULL;
  } else {
    while (next->next) {
      next = next->next;
    }
    next->next      = ilink;
    ilink->previous = next;
  }
  jac->nsplits++;

  PetscFunctionReturn(0);
}
EXTERN_C_END

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetFields"
/*@
    PCFieldSplitSetFields - Sets the fields for one particular split in the field split preconditioner

    Collective on PC

    Input Parameters:
+   pc  - the preconditioner context
.   n - the number of fields in this split
.   fields - the fields in this split

    Level: intermediate

    Notes: Use PCFieldSplitSetIS() to set a completely general set of indices as a field.

     The PCFieldSplitSetFields() is for defining fields as a strided blocks. For example, if the block
     size is three then one can define a field as 0, or 1 or 2 or 0,1 or 0,2 or 1,2 which mean
     0xx3xx6xx9xx12 ... x1xx4xx7xx ... xx2xx5xx8xx.. 01x34x67x... 0x1x3x5x7.. x12x45x78x....
     where the numbered entries indicate what is in the field.

.seealso: PCFieldSplitGetSubKSP(), PCFIELDSPLIT, PCFieldSplitSetBlockSize(), PCFieldSplitSetIS()

@*/
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetFields(PC pc,PetscInt n, PetscInt *fields)
{
  PetscErrorCode ierr,(*f)(PC,PetscInt,PetscInt *);

  PetscFunctionBegin;
  PetscValidHeaderSpecific(pc,PC_COOKIE,1);
  ierr = PetscObjectQueryFunction((PetscObject)pc,"PCFieldSplitSetFields_C",(void (**)(void))&f);CHKERRQ(ierr);
  if (f) {
    ierr = (*f)(pc,n,fields);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetIS"
/*@
    PCFieldSplitSetIS - Sets the exact elements for field

    Collective on PC

    Input Parameters:
+   pc  - the preconditioner context
.   is - the index set that defines the vector elements in this field


    Notes: Use PCFieldSplitSetFields(), for fields defined by strided types.

    Level: intermediate

.seealso: PCFieldSplitGetSubKSP(), PCFIELDSPLIT, PCFieldSplitSetBlockSize()

@*/
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetIS(PC pc,IS is)
{
  PetscErrorCode ierr,(*f)(PC,IS);

  PetscFunctionBegin;
  PetscValidHeaderSpecific(pc,PC_COOKIE,1);
  PetscValidHeaderSpecific(is,IS_COOKIE,1);
  ierr = PetscObjectQueryFunction((PetscObject)pc,"PCFieldSplitSetIS_C",(void (**)(void))&f);CHKERRQ(ierr);
  if (f) {
    ierr = (*f)(pc,is);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetBlockSize"
/*@
    PCFieldSplitSetBlockSize - Sets the block size for defining where fields start in the
      fieldsplit preconditioner. If not set the matrix block size is used.

    Collective on PC

    Input Parameters:
+   pc  - the preconditioner context
-   bs - the block size

    Level: intermediate

.seealso: PCFieldSplitGetSubKSP(), PCFIELDSPLIT, PCFieldSplitSetFields()

@*/
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetBlockSize(PC pc,PetscInt bs)
{
  PetscErrorCode ierr,(*f)(PC,PetscInt);

  PetscFunctionBegin;
  PetscValidHeaderSpecific(pc,PC_COOKIE,1);
  ierr = PetscObjectQueryFunction((PetscObject)pc,"PCFieldSplitSetBlockSize_C",(void (**)(void))&f);CHKERRQ(ierr);
  if (f) {
    ierr = (*f)(pc,bs);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitGetSubKSP"
/*@C
   PCFieldSplitGetSubKSP - Gets the KSP contexts for all splits

   Collective on KSP

   Input Parameter:
.  pc - the preconditioner context

   Output Parameters:
+  n - the number of split
-  pc - the array of KSP contexts

   Note:
   After PCFieldSplitGetSubKSP() the array of KSPs IS to be freed by the user
   (not the KSP just the array that contains them).

   You must call KSPSetUp() before calling PCFieldSplitGetSubKSP().

   Level: advanced

.seealso: PCFIELDSPLIT
@*/
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitGetSubKSP(PC pc,PetscInt *n,KSP *subksp[])
{
  PetscErrorCode ierr,(*f)(PC,PetscInt*,KSP **);

  PetscFunctionBegin;
  PetscValidHeaderSpecific(pc,PC_COOKIE,1);
  PetscValidIntPointer(n,2);
  ierr = PetscObjectQueryFunction((PetscObject)pc,"PCFieldSplitGetSubKSP_C",(void (**)(void))&f);CHKERRQ(ierr);
  if (f) {
    ierr = (*f)(pc,n,subksp);CHKERRQ(ierr);
  } else {
    SETERRQ(PETSC_ERR_ARG_WRONG,"Cannot get subksp for this type of PC");
  }
  PetscFunctionReturn(0);
}

EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetType_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetType_FieldSplit(PC pc,PCCompositeType type)
{
  PC_FieldSplit  *jac = (PC_FieldSplit*)pc->data;

  PetscFunctionBegin;
  jac->type = type;
  PetscFunctionReturn(0);
}
EXTERN_C_END

EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetBlockSize_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetBlockSize_FieldSplit(PC pc,PetscInt bs)
{
  PC_FieldSplit  *jac = (PC_FieldSplit*)pc->data;

  PetscFunctionBegin;
  if (bs < 1) SETERRQ1(PETSC_ERR_ARG_OUTOFRANGE,"Blocksize must be positive, you gave %D",bs);
  if (jac->bs > 0 && jac->bs != bs) SETERRQ2(PETSC_ERR_ARG_WRONGSTATE,"Cannot change fieldsplit blocksize from %D to %D after it has been set",jac->bs,bs);
  jac->bs = bs;
  PetscFunctionReturn(0);
}
EXTERN_C_END

#undef __FUNCT__
#define __FUNCT__ "PCFieldSplitSetType"
/*@
   PCFieldSplitSetType - Sets the type of fieldsplit preconditioner.

   Collective on PC

   Input Parameter:
.  pc - the preconditioner context
.  type - PC_COMPOSITE_ADDITIVE (default), PC_COMPOSITE_MULTIPLICATIVE, PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE

   Options Database Key:
.  -pc_fieldsplit_type <type: one of multiplicative, additive, symmetric_multiplicative, special> - Sets fieldsplit preconditioner type

   Level: Developer

.keywords: PC, set, type, composite preconditioner, additive, multiplicative

.seealso: PCCompositeSetType()

@*/
PetscErrorCode PETSCKSP_DLLEXPORT PCFieldSplitSetType(PC pc,PCCompositeType type)
{
  PetscErrorCode ierr,(*f)(PC,PCCompositeType);

  PetscFunctionBegin;
  PetscValidHeaderSpecific(pc,PC_COOKIE,1);
  ierr = PetscObjectQueryFunction((PetscObject)pc,"PCFieldSplitSetType_C",(void (**)(void))&f);CHKERRQ(ierr);
  if (f) {
    ierr = (*f)(pc,type);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

/* -------------------------------------------------------------------------------------*/
/*MC
   PCFIELDSPLIT - Preconditioner created by combining separate preconditioners for individual
                  fields or groups of fields


     To set options on the solvers for each block append -sub_ to all the PC
        options database keys. For example, -sub_pc_type ilu -sub_pc_factor_levels 1

     To set the options on the solvers separate for each block call PCFieldSplitGetSubKSP()
         and set the options directly on the resulting KSP object

   Level: intermediate

   Options Database Keys:
+   -pc_splitfield_%d_fields <a,b,..> - indicates the fields to be used in the %d'th split
.   -pc_splitfield_default - automatically add any fields to additional splits that have not
                              been supplied explicitly by -pc_splitfield_%d_fields
.   -pc_splitfield_block_size <bs> - size of block that defines fields (i.e. there are bs fields)
-   -pc_splitfield_type <additive,multiplicative>

   Notes: use PCFieldSplitSetFields() to set fields defined by "strided" entries and PCFieldSplitSetIS()
     to define a field by an arbitrary collection of entries.

      If no fields are set the default is used. The fields are defined by entries strided by bs,
      beginning at 0 then 1, etc to bs-1. The block size can be set with PCFieldSplitSetBlockSize(),
      if this is not called the block size defaults to the blocksize of the second matrix passed
      to KSPSetOperators()/PCSetOperators().

      Currently for the multiplicative version, the updated residual needed for the next field
     solve is computed via a matrix vector product over the entire array. An optimization would be
     to update the residual only for the part of the right hand side associated with the next field
     solve. (This would involve more MatGetSubMatrix() calls or some other mechanism to compute the
     part of the matrix needed to just update part of the residual).

   Concepts: physics based preconditioners

.seealso:  PCCreate(), PCSetType(), PCType (for list of available types), PC,
           PCFieldSplitGetSubKSP(), PCFieldSplitSetFields(), PCFieldSplitSetType(), PCFieldSplitSetIS()
M*/

EXTERN_C_BEGIN
#undef __FUNCT__
#define __FUNCT__ "PCCreate_FieldSplit"
PetscErrorCode PETSCKSP_DLLEXPORT PCCreate_FieldSplit(PC pc)
{
  PetscErrorCode ierr;
  PC_FieldSplit  *jac;

  PetscFunctionBegin;
  ierr = PetscNewLog(pc,PC_FieldSplit,&jac);CHKERRQ(ierr);
  jac->bs        = -1;
  jac->nsplits   = 0;
  jac->type      = PC_COMPOSITE_ADDITIVE;

  pc->data     = (void*)jac;

  pc->ops->apply             = PCApply_FieldSplit;
  pc->ops->applytranspose    = PCApplyTranspose_FieldSplit;
  pc->ops->setup             = PCSetUp_FieldSplit;
  pc->ops->destroy           = PCDestroy_FieldSplit;
  pc->ops->setfromoptions    = PCSetFromOptions_FieldSplit;
  pc->ops->view              = PCView_FieldSplit;
  pc->ops->applyrichardson   = 0;

  ierr = PetscObjectComposeFunctionDynamic((PetscObject)pc,"PCFieldSplitGetSubKSP_C","PCFieldSplitGetSubKSP_FieldSplit",
                    PCFieldSplitGetSubKSP_FieldSplit);CHKERRQ(ierr);
  ierr = PetscObjectComposeFunctionDynamic((PetscObject)pc,"PCFieldSplitSetFields_C","PCFieldSplitSetFields_FieldSplit",
                    PCFieldSplitSetFields_FieldSplit);CHKERRQ(ierr);
  ierr = PetscObjectComposeFunctionDynamic((PetscObject)pc,"PCFieldSplitSetIS_C","PCFieldSplitSetIS_FieldSplit",
                    PCFieldSplitSetIS_FieldSplit);CHKERRQ(ierr);
  ierr = PetscObjectComposeFunctionDynamic((PetscObject)pc,"PCFieldSplitSetType_C","PCFieldSplitSetType_FieldSplit",
                    PCFieldSplitSetType_FieldSplit);CHKERRQ(ierr);
  ierr = PetscObjectComposeFunctionDynamic((PetscObject)pc,"PCFieldSplitSetBlockSize_C","PCFieldSplitSetBlockSize_FieldSplit",
                    PCFieldSplitSetBlockSize_FieldSplit);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}
EXTERN_C_END