xref: /petsc/src/mat/impls/dense/mpi/mpidense.c (revision 39ddd567ee2cd5629f9b2e9aadacf11d968d0842)

#ifndef lint
static char vcid[] = "$Id: mpidense.c,v 1.1 1995/10/19 22:14:22 curfman Exp curfman $";
#endif

#include "mpidense.h"
#include "vec/vecimpl.h"
#include "inline/spops.h"

static int MatSetValues_MPIDense(Mat mat,int m,int *idxm,int n,
                               int *idxn,Scalar *v,InsertMode addv)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  int          ierr, i, j, rstart = mdn->rstart, rend = mdn->rend, row;

  if (mdn->insertmode != NOT_SET_VALUES && mdn->insertmode != addv) {
    SETERRQ(1,"MatSetValues_MPIDense:Cannot mix inserts and adds");
  }
  mdn->insertmode = addv;
  for ( i=0; i<m; i++ ) {
    if (idxm[i] < 0) SETERRQ(1,"MatSetValues_MPIDense:Negative row");
    if (idxm[i] >= mdn->M) SETERRQ(1,"MatSetValues_MPIDense:Row too large");
    if (idxm[i] >= rstart && idxm[i] < rend) {
      row = idxm[i] - rstart;
      for ( j=0; j<n; j++ ) {
        if (idxn[j] < 0) SETERRQ(1,"MatSetValues_MPIDense:Negative column");
        if (idxn[j] >= mdn->N)
          SETERRQ(1,"MatSetValues_MPIDense:Column too large");
        ierr = MatSetValues(mdn->A,1,&row,1,&idxn[j],v+i*n+j,addv);
        CHKERRQ(ierr);
      }
    }
    else {
      ierr = StashValues_Private(&mdn->stash,idxm[i],n,idxn,v+i*n,addv);
      CHKERRQ(ierr);
    }
  }
  return 0;
}

static int MatAssemblyBegin_MPIDense(Mat mat,MatAssemblyType mode)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  MPI_Comm     comm = mat->comm;
  int          size = mdn->size, *owners = mdn->rowners, rank = mdn->rank;
  int          *nprocs,i,j,idx,*procs,nsends,nreceives,nmax,*work;
  int          tag = mat->tag, *owner,*starts,count,ierr;
  InsertMode   addv;
  MPI_Request  *send_waits,*recv_waits;
  Scalar       *rvalues,*svalues;

  /* make sure all processors are either in INSERTMODE or ADDMODE */
  MPI_Allreduce((void *) &mdn->insertmode,(void *) &addv,1,MPI_INT,
                MPI_BOR,comm);
  if (addv == (ADD_VALUES|INSERT_VALUES)) { SETERRQ(1,
    "MatAssemblyBegin_MPIDense:Cannot mix adds/inserts on different procs");
    }
  mdn->insertmode = addv; /* in case this processor had no cache */

  /*  first count number of contributors to each processor */
  nprocs = (int *) PETSCMALLOC( 2*size*sizeof(int) ); CHKPTRQ(nprocs);
  PetscZero(nprocs,2*size*sizeof(int)); procs = nprocs + size;
  owner = (int *) PETSCMALLOC( (mdn->stash.n+1)*sizeof(int) ); CHKPTRQ(owner);
  for ( i=0; i<mdn->stash.n; i++ ) {
    idx = mdn->stash.idx[i];
    for ( j=0; j<size; j++ ) {
      if (idx >= owners[j] && idx < owners[j+1]) {
        nprocs[j]++; procs[j] = 1; owner[i] = j; break;
      }
    }
  }
  nsends = 0;  for ( i=0; i<size; i++ ) { nsends += procs[i];}

  /* inform other processors of number of messages and max length*/
  work = (int *) PETSCMALLOC( size*sizeof(int) ); CHKPTRQ(work);
  MPI_Allreduce((void *) procs,(void *) work,size,MPI_INT,MPI_SUM,comm);
  nreceives = work[rank];
  MPI_Allreduce((void *) nprocs,(void *) work,size,MPI_INT,MPI_MAX,comm);
  nmax = work[rank];
  PETSCFREE(work);

  /* post receives:
       1) each message will consist of ordered pairs
     (global index,value) we store the global index as a double
     to simplify the message passing.
       2) since we don't know how long each individual message is we
     allocate the largest needed buffer for each receive. Potentially
     this is a lot of wasted space.

       This could be done better.
  */
  rvalues = (Scalar *) PETSCMALLOC(3*(nreceives+1)*(nmax+1)*sizeof(Scalar));
  CHKPTRQ(rvalues);
  recv_waits = (MPI_Request *) PETSCMALLOC((nreceives+1)*sizeof(MPI_Request));
  CHKPTRQ(recv_waits);
  for ( i=0; i<nreceives; i++ ) {
    MPI_Irecv((void *)(rvalues+3*nmax*i),3*nmax,MPIU_SCALAR,MPI_ANY_SOURCE,tag,
              comm,recv_waits+i);
  }

  /* do sends:
      1) starts[i] gives the starting index in svalues for stuff going to
         the ith processor
  */
  svalues = (Scalar *) PETSCMALLOC( 3*(mdn->stash.n+1)*sizeof(Scalar) );
  CHKPTRQ(svalues);
  send_waits = (MPI_Request *) PETSCMALLOC( (nsends+1)*sizeof(MPI_Request));
  CHKPTRQ(send_waits);
  starts = (int *) PETSCMALLOC( size*sizeof(int) ); CHKPTRQ(starts);
  starts[0] = 0;
  for ( i=1; i<size; i++ ) { starts[i] = starts[i-1] + nprocs[i-1];}
  for ( i=0; i<mdn->stash.n; i++ ) {
    svalues[3*starts[owner[i]]]       = (Scalar)  mdn->stash.idx[i];
    svalues[3*starts[owner[i]]+1]     = (Scalar)  mdn->stash.idy[i];
    svalues[3*(starts[owner[i]]++)+2] =  mdn->stash.array[i];
  }
  PETSCFREE(owner);
  starts[0] = 0;
  for ( i=1; i<size; i++ ) { starts[i] = starts[i-1] + nprocs[i-1];}
  count = 0;
  for ( i=0; i<size; i++ ) {
    if (procs[i]) {
      MPI_Isend((void*)(svalues+3*starts[i]),3*nprocs[i],MPIU_SCALAR,i,tag,
                comm,send_waits+count++);
    }
  }
  PETSCFREE(starts); PETSCFREE(nprocs);

  /* Free cache space */
  ierr = StashDestroy_Private(&mdn->stash); CHKERRQ(ierr);

  mdn->svalues    = svalues;    mdn->rvalues = rvalues;
  mdn->nsends     = nsends;     mdn->nrecvs = nreceives;
  mdn->send_waits = send_waits; mdn->recv_waits = recv_waits;
  mdn->rmax       = nmax;

  return 0;
}
extern int MatSetUpMultiply_MPIDense(Mat);

static int MatAssemblyEnd_MPIDense(Mat mat,MatAssemblyType mode)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  MPI_Status   *send_status,recv_status;
  int          imdex, nrecvs=mdn->nrecvs, count=nrecvs, i, n, ierr, row, col;
  Scalar       *values,val;
  InsertMode   addv = mdn->insertmode;

  /*  wait on receives */
  while (count) {
    MPI_Waitany(nrecvs,mdn->recv_waits,&imdex,&recv_status);
    /* unpack receives into our local space */
    values = mdn->rvalues + 3*imdex*mdn->rmax;
    MPI_Get_count(&recv_status,MPIU_SCALAR,&n);
    n = n/3;
    for ( i=0; i<n; i++ ) {
      row = (int) PETSCREAL(values[3*i]) - mdn->rstart;
      col = (int) PETSCREAL(values[3*i+1]);
      val = values[3*i+2];
      if (col >= 0 && col < mdn->N) {
        MatSetValues(mdn->A,1,&row,1,&col,&val,addv);
      }
      else {SETERRQ(1,"MatAssemblyEnd_MPIDense:Invalid column");}
    }
    count--;
  }
  PETSCFREE(mdn->recv_waits); PETSCFREE(mdn->rvalues);

  /* wait on sends */
  if (mdn->nsends) {
    send_status = (MPI_Status *) PETSCMALLOC( mdn->nsends*sizeof(MPI_Status) );
    CHKPTRQ(send_status);
    MPI_Waitall(mdn->nsends,mdn->send_waits,send_status);
    PETSCFREE(send_status);
  }
  PETSCFREE(mdn->send_waits); PETSCFREE(mdn->svalues);

  mdn->insertmode = NOT_SET_VALUES;
  ierr = MatAssemblyBegin(mdn->A,mode); CHKERRQ(ierr);
  ierr = MatAssemblyEnd(mdn->A,mode); CHKERRQ(ierr);

  if (!mdn->assembled && mode == FINAL_ASSEMBLY) {
    ierr = MatSetUpMultiply_MPIDense(mat); CHKERRQ(ierr);
  }
  mdn->assembled = 1;
  return 0;
}

static int MatZeroEntries_MPIDense(Mat A)
{
  Mat_MPIDense *l = (Mat_MPIDense *) A->data;
  return MatZeroEntries(l->A);
}

/* the code does not do the diagonal entries correctly unless the
   matrix is square and the column and row owerships are identical.
   This is a BUG. The only way to fix it seems to be to access
   aij->A and aij->B directly and not through the MatZeroRows()
   routine.
*/
static int MatZeroRows_MPIDense(Mat A,IS is,Scalar *diag)
{
  Mat_MPIDense   *l = (Mat_MPIDense *) A->data;
  int            i,ierr,N, *rows,*owners = l->rowners,size = l->size;
  int            *procs,*nprocs,j,found,idx,nsends,*work;
  int            nmax,*svalues,*starts,*owner,nrecvs,rank = l->rank;
  int            *rvalues,tag = A->tag,count,base,slen,n,*source;
  int            *lens,imdex,*lrows,*values;
  MPI_Comm       comm = A->comm;
  MPI_Request    *send_waits,*recv_waits;
  MPI_Status     recv_status,*send_status;
  IS             istmp;

  if (!l->assembled) SETERRQ(1,"MatZeroRows_MPIDense:Must assemble matrix");
  ierr = ISGetLocalSize(is,&N); CHKERRQ(ierr);
  ierr = ISGetIndices(is,&rows); CHKERRQ(ierr);

  /*  first count number of contributors to each processor */
  nprocs = (int *) PETSCMALLOC( 2*size*sizeof(int) ); CHKPTRQ(nprocs);
  PetscZero(nprocs,2*size*sizeof(int)); procs = nprocs + size;
  owner = (int *) PETSCMALLOC((N+1)*sizeof(int)); CHKPTRQ(owner); /* see note*/
  for ( i=0; i<N; i++ ) {
    idx = rows[i];
    found = 0;
    for ( j=0; j<size; j++ ) {
      if (idx >= owners[j] && idx < owners[j+1]) {
        nprocs[j]++; procs[j] = 1; owner[i] = j; found = 1; break;
      }
    }
    if (!found) SETERRQ(1,"MatZeroRows_MPIDense:Index out of range");
  }
  nsends = 0;  for ( i=0; i<size; i++ ) { nsends += procs[i];}

  /* inform other processors of number of messages and max length*/
  work = (int *) PETSCMALLOC( size*sizeof(int) ); CHKPTRQ(work);
  MPI_Allreduce( procs, work,size,MPI_INT,MPI_SUM,comm);
  nrecvs = work[rank];
  MPI_Allreduce( nprocs, work,size,MPI_INT,MPI_MAX,comm);
  nmax = work[rank];
  PETSCFREE(work);

  /* post receives:   */
  rvalues = (int *) PETSCMALLOC((nrecvs+1)*(nmax+1)*sizeof(int)); /*see note */
  CHKPTRQ(rvalues);
  recv_waits = (MPI_Request *) PETSCMALLOC((nrecvs+1)*sizeof(MPI_Request));
  CHKPTRQ(recv_waits);
  for ( i=0; i<nrecvs; i++ ) {
    MPI_Irecv(rvalues+nmax*i,nmax,MPI_INT,MPI_ANY_SOURCE,tag,comm,recv_waits+i);
  }

  /* do sends:
      1) starts[i] gives the starting index in svalues for stuff going to
         the ith processor
  */
  svalues = (int *) PETSCMALLOC( (N+1)*sizeof(int) ); CHKPTRQ(svalues);
  send_waits = (MPI_Request *) PETSCMALLOC( (nsends+1)*sizeof(MPI_Request));
  CHKPTRQ(send_waits);
  starts = (int *) PETSCMALLOC( (size+1)*sizeof(int) ); CHKPTRQ(starts);
  starts[0] = 0;
  for ( i=1; i<size; i++ ) { starts[i] = starts[i-1] + nprocs[i-1];}
  for ( i=0; i<N; i++ ) {
    svalues[starts[owner[i]]++] = rows[i];
  }
  ISRestoreIndices(is,&rows);

  starts[0] = 0;
  for ( i=1; i<size+1; i++ ) { starts[i] = starts[i-1] + nprocs[i-1];}
  count = 0;
  for ( i=0; i<size; i++ ) {
    if (procs[i]) {
      MPI_Isend(svalues+starts[i],nprocs[i],MPI_INT,i,tag,comm,send_waits+count++);
    }
  }
  PETSCFREE(starts);

  base = owners[rank];

  /*  wait on receives */
  lens   = (int *) PETSCMALLOC( 2*(nrecvs+1)*sizeof(int) ); CHKPTRQ(lens);
  source = lens + nrecvs;
  count  = nrecvs; slen = 0;
  while (count) {
    MPI_Waitany(nrecvs,recv_waits,&imdex,&recv_status);
    /* unpack receives into our local space */
    MPI_Get_count(&recv_status,MPI_INT,&n);
    source[imdex]  = recv_status.MPI_SOURCE;
    lens[imdex]  = n;
    slen += n;
    count--;
  }
  PETSCFREE(recv_waits);

  /* move the data into the send scatter */
  lrows = (int *) PETSCMALLOC( (slen+1)*sizeof(int) ); CHKPTRQ(lrows);
  count = 0;
  for ( i=0; i<nrecvs; i++ ) {
    values = rvalues + i*nmax;
    for ( j=0; j<lens[i]; j++ ) {
      lrows[count++] = values[j] - base;
    }
  }
  PETSCFREE(rvalues); PETSCFREE(lens);
  PETSCFREE(owner); PETSCFREE(nprocs);

  /* actually zap the local rows */
  ierr = ISCreateSeq(MPI_COMM_SELF,slen,lrows,&istmp);CHKERRQ(ierr);
  PLogObjectParent(A,istmp);
  PETSCFREE(lrows);
  ierr = MatZeroRows(l->A,istmp,diag); CHKERRQ(ierr);
  ierr = ISDestroy(istmp); CHKERRQ(ierr);

  /* wait on sends */
  if (nsends) {
    send_status = (MPI_Status *) PETSCMALLOC(nsends*sizeof(MPI_Status));
    CHKPTRQ(send_status);
    MPI_Waitall(nsends,send_waits,send_status);
    PETSCFREE(send_status);
  }
  PETSCFREE(send_waits); PETSCFREE(svalues);

  return 0;
}

static int MatMult_MPIDense(Mat mat,Vec xx,Vec yy)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  int          ierr;
  if (!mdn->assembled)
    SETERRQ(1,"MatMult_MPIDense:Must assemble matrix first");
  ierr = VecScatterBegin(xx,mdn->lvec,INSERT_VALUES,SCATTER_ALL,mdn->Mvctx);
  CHKERRQ(ierr);
  ierr = VecScatterEnd(xx,mdn->lvec,INSERT_VALUES,SCATTER_ALL,mdn->Mvctx);
  CHKERRQ(ierr);
  ierr = MatMult(mdn->A,mdn->lvec,yy); CHKERRQ(ierr);
  return 0;
}

static int MatMultAdd_MPIDense(Mat mat,Vec xx,Vec yy,Vec zz)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  int          ierr;
  if (!mdn->assembled)
    SETERRQ(1,"MatMultAdd_MPIDense:Must assemble matrix first");
  ierr = VecScatterBegin(xx,mdn->lvec,ADD_VALUES,SCATTER_ALL,mdn->Mvctx);
  CHKERRQ(ierr);
  ierr = VecScatterEnd(xx,mdn->lvec,ADD_VALUES,SCATTER_ALL,mdn->Mvctx);
  CHKERRQ(ierr);
  ierr = MatMultAdd(mdn->A,mdn->lvec,yy,zz); CHKERRQ(ierr);
  return 0;
}

/*
  This only works correctly for square matrices where the subblock A->A is the
   diagonal block
*/
static int MatGetDiagonal_MPIDense(Mat A,Vec v)
{
  Mat_MPIDense *a = (Mat_MPIDense *) A->data;
  if (!a->assembled) SETERRQ(1,"MatGetDiag_MPIDense:must assemble matrix");
  return MatGetDiagonal(a->A,v);
}

static int MatDestroy_MPIDense(PetscObject obj)
{
  Mat          mat = (Mat) obj;
  Mat_MPIDense *aij = (Mat_MPIDense *) mat->data;
  int          ierr;
#if defined(PETSC_LOG)
  PLogObjectState(obj,"Rows=%d, Cols=%d",aij->M,aij->N);
#endif
  PETSCFREE(aij->rowners);
  ierr = MatDestroy(aij->A); CHKERRQ(ierr);
  if (aij->lvec)   VecDestroy(aij->lvec);
  if (aij->Mvctx)  VecScatterCtxDestroy(aij->Mvctx);
  PETSCFREE(aij);
  PLogObjectDestroy(mat);
  PETSCHEADERDESTROY(mat);
  return 0;
}

#include "pinclude/pviewer.h"

static int MatView_MPIDense_Binary(Mat mat,Viewer viewer)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  int          ierr;
  if (mdn->size == 1) {
    ierr = MatView(mdn->A,viewer); CHKERRQ(ierr);
  }
  else SETERRQ(1,"MatView_MPIDense_Binary:Only uniprocessor output supported");
  return 0;
}

static int MatView_MPIDense_ASCII(Mat mat,Viewer viewer)
{
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  int          ierr, format;
  PetscObject  vobj = (PetscObject) viewer;
  FILE         *fd;

  if (vobj->type == ASCII_FILE_VIEWER || vobj->type == ASCII_FILES_VIEWER) {
    ierr = ViewerFileGetFormat_Private(viewer,&format);
    if (format == FILE_FORMAT_INFO) {
      ; /* do nothing for now */
    }
  }

  if (vobj->type == ASCII_FILE_VIEWER) {
    ierr = ViewerFileGetPointer_Private(viewer,&fd); CHKERRQ(ierr);
    MPIU_Seq_begin(mat->comm,1);
    fprintf(fd,"[%d] rows %d starts %d ends %d cols %d\n",
             mdn->rank,mdn->m,mdn->rstart,mdn->rend,mdn->n);
    ierr = MatView(mdn->A,viewer); CHKERRQ(ierr);
    fflush(fd);
    MPIU_Seq_end(mat->comm,1);
  }
  else {
    int size = mdn->size, rank = mdn->rank;
    if (size == 1) {
      ierr = MatView(mdn->A,viewer); CHKERRQ(ierr);
    }
    else {
      /* assemble the entire matrix onto first processor. */
      Mat       A;
      int       M = mdn->M, N = mdn->N,m,row,i, nz, *cols;
      Scalar    *vals;
      Mat_SeqDense *Amdn = (Mat_SeqDense*) mdn->A->data;

      if (!rank) {
        ierr = MatCreateMPIDense(mat->comm,M,M,N,N,&A); CHKERRQ(ierr);
      }
      else {
        ierr = MatCreateMPIDense(mat->comm,0,M,N,N,&A); CHKERRQ(ierr);
      }
      PLogObjectParent(mat,A);

      /* Copy the matrix ... This isn't the most efficient means,
         but it's quick for now */
      row = mdn->rstart; m = Amdn->m;
      for ( i=0; i<m; i++ ) {
        ierr = MatGetRow(mat,row,&nz,&cols,&vals); CHKERRQ(ierr);
        ierr = MatSetValues(A,1,&row,nz,cols,vals,INSERT_VALUES); CHKERRQ(ierr);
        ierr = MatRestoreRow(mat,row,&nz,&cols,&vals); CHKERRQ(ierr);
        row++;
      }

      ierr = MatAssemblyBegin(A,FINAL_ASSEMBLY); CHKERRQ(ierr);
      ierr = MatAssemblyEnd(A,FINAL_ASSEMBLY); CHKERRQ(ierr);
      if (!rank) {
        ierr = MatView(((Mat_MPIDense*)(A->data))->A,viewer); CHKERRQ(ierr);
      }
      ierr = MatDestroy(A); CHKERRQ(ierr);
    }
  }
  return 0;
}

static int MatView_MPIDense(PetscObject obj,Viewer viewer)
{
  Mat          mat = (Mat) obj;
  Mat_MPIDense *mdn = (Mat_MPIDense *) mat->data;
  PetscObject  vobj = (PetscObject) viewer;
  int          ierr;

  if (!mdn->assembled) SETERRQ(1,"MatView_MPIDense:must assemble matrix");
  if (!viewer) {
    viewer = STDOUT_VIEWER_SELF; vobj = (PetscObject) viewer;
  }
  if (vobj->cookie == VIEWER_COOKIE && vobj->type == ASCII_FILE_VIEWER) {
    ierr = MatView_MPIDense_ASCII(mat,viewer); CHKERRQ(ierr);
  }
  else if (vobj->cookie == VIEWER_COOKIE && vobj->type == ASCII_FILES_VIEWER) {
    ierr = MatView_MPIDense_ASCII(mat,viewer); CHKERRQ(ierr);
  }
  else if (vobj->type == BINARY_FILE_VIEWER) {
    return MatView_MPIDense_Binary(mat,viewer);
  }
  return 0;
}

static int MatGetInfo_MPIDense(Mat matin,MatInfoType flag,int *nz,
                             int *nzalloc,int *mem)
{
  Mat_MPIDense *mat = (Mat_MPIDense *) matin->data;
  Mat          A = mat->A;
  int          ierr, isend[3], irecv[3];

  ierr = MatGetInfo(A,MAT_LOCAL,&isend[0],&isend[1],&isend[2]); CHKERRQ(ierr);
  if (flag == MAT_LOCAL) {
    *nz = isend[0]; *nzalloc = isend[1]; *mem = isend[2];
  } else if (flag == MAT_GLOBAL_MAX) {
    MPI_Allreduce( isend, irecv,3,MPI_INT,MPI_MAX,matin->comm);
    *nz = irecv[0]; *nzalloc = irecv[1]; *mem = irecv[2];
  } else if (flag == MAT_GLOBAL_SUM) {
    MPI_Allreduce( isend, irecv,3,MPI_INT,MPI_SUM,matin->comm);
    *nz = irecv[0]; *nzalloc = irecv[1]; *mem = irecv[2];
  }
  return 0;
}

static int MatSetOption_MPIDense(Mat A,MatOption op)
{
  Mat_MPIDense *a = (Mat_MPIDense *) A->data;

  if (op == NO_NEW_NONZERO_LOCATIONS ||
      op == YES_NEW_NONZERO_LOCATIONS ||
      op == COLUMNS_SORTED ||
      op == ROW_ORIENTED) {
        MatSetOption(a->A,op);
  }
  else if (op == ROWS_SORTED ||
           op == SYMMETRIC_MATRIX ||
           op == STRUCTURALLY_SYMMETRIC_MATRIX ||
           op == YES_NEW_DIAGONALS)
    PLogInfo((PetscObject)A,"Info:MatSetOption_MPIDense:Option ignored\n");
  else if (op == COLUMN_ORIENTED)
    {SETERRQ(PETSC_ERR_SUP,"MatSetOption_MPIDense:COLUMN_ORIENTED");}
  else if (op == NO_NEW_DIAGONALS)
    {SETERRQ(PETSC_ERR_SUP,"MatSetOption_MPIDense:NO_NEW_DIAGONALS");}
  else
    {SETERRQ(PETSC_ERR_SUP,"MatSetOption_MPIDense:unknown option");}
  return 0;
}

static int MatGetSize_MPIDense(Mat matin,int *m,int *n)
{
  Mat_MPIDense *mat = (Mat_MPIDense *) matin->data;
  *m = mat->M; *n = mat->N;
  return 0;
}

static int MatGetLocalSize_MPIDense(Mat matin,int *m,int *n)
{
  Mat_MPIDense *mat = (Mat_MPIDense *) matin->data;
  *m = mat->m; *n = mat->N;
  return 0;
}

static int MatGetOwnershipRange_MPIDense(Mat matin,int *m,int *n)
{
  Mat_MPIDense *mat = (Mat_MPIDense *) matin->data;
  *m = mat->rstart; *n = mat->rend;
  return 0;
}

static int MatGetRow_MPIDense(Mat matin,int row,int *nz,int **idx,Scalar **v)
{
  Mat_MPIDense *mat = (Mat_MPIDense *) matin->data;
  int          lrow, rstart = mat->rstart, rend = mat->rend;

  if (row < rstart || row >= rend) SETERRQ(1,"MatGetRow_MPIDense:only local rows")
  lrow = row - rstart;
  return MatGetRow(mat->A,lrow,nz,idx,v);
}

static int MatRestoreRow_MPIDense(Mat mat,int row,int *nz,int **idx,Scalar **v)
{
  if (idx) PETSCFREE(*idx);
  if (v) PETSCFREE(*v);
  return 0;
}

static int MatCopyPrivate_MPIDense(Mat,Mat *);

/* -------------------------------------------------------------------*/
static struct _MatOps MatOps = {MatSetValues_MPIDense,
       MatGetRow_MPIDense,MatRestoreRow_MPIDense,
       MatMult_MPIDense,MatMultAdd_MPIDense,
       0, 0,
       0, 0,
       0, 0, 0,
       0, 0, 0,
       MatGetInfo_MPIDense, 0,
       MatGetDiagonal_MPIDense, 0, 0,
       MatAssemblyBegin_MPIDense,MatAssemblyEnd_MPIDense,
       0,
       MatSetOption_MPIDense,MatZeroEntries_MPIDense,MatZeroRows_MPIDense,
       0,
       0, 0, 0, 0,
       MatGetSize_MPIDense,MatGetLocalSize_MPIDense,
       MatGetOwnershipRange_MPIDense,
       0, 0,
       0, 0, 0, 0, 0, MatCopyPrivate_MPIDense};

/*@C
   MatCreateMPIDense - Creates a sparse parallel matrix in dense format.

   Input Parameters:
.  comm - MPI communicator
.  m - number of local rows (or PETSC_DECIDE to have calculated if M is given)
.  n - number of local columns (or PETSC_DECIDE to have calculated
           if N is given)
.  M - number of global rows (or PETSC_DECIDE to have calculated if m is given)
.  N - number of global columns (or PETSC_DECIDE to have calculated
           if n is given)

   Output Parameter:
.  newmat - the matrix

   Notes:
   The dense format is fully compatible with standard Fortran 77
   storage by columns.

   The user MUST specify either the local or global matrix dimensions
   (possibly both).

.keywords: matrix, dense, parallel

.seealso: MatCreate(), MatCreateSeqDense(), MatSetValues()
@*/
int MatCreateMPIDense(MPI_Comm comm,int m,int n,int M,int N,Mat *newmat)
{
  Mat          mat;
  Mat_MPIDense *a;
  int          ierr, i;

  *newmat         = 0;
  PETSCHEADERCREATE(mat,_Mat,MAT_COOKIE,MATMPIDENSE,comm);
  PLogObjectCreate(mat);
  mat->data       = (void *) (a = PETSCNEW(Mat_MPIDense)); CHKPTRQ(a);
  PetscMemcpy(&mat->ops,&MatOps,sizeof(struct _MatOps));
  mat->destroy    = MatDestroy_MPIDense;
  mat->view       = MatView_MPIDense;
  mat->factor     = 0;

  a->insertmode = NOT_SET_VALUES;
  MPI_Comm_rank(comm,&a->rank);
  MPI_Comm_size(comm,&a->size);

  if (M == PETSC_DECIDE) MPI_Allreduce(&m,&M,1,MPI_INT,MPI_SUM,comm);
  if (m == PETSC_DECIDE) {m = M/a->size + ((M % a->size) > a->rank);}

  /* each row stores all columns */
  if (N == PETSC_DECIDE) N = n;
  if (n == PETSC_DECIDE) n = N;
  if (n != N) SETERRQ(1,"MatCreateMPIDense:For now, only n=N is supported");
  a->N = N;
  a->M = M;
  a->m = m;
  a->n = n;

  /* build local table of row and column ownerships */
  a->rowners = (int *) PETSCMALLOC((a->size+2)*sizeof(int)); CHKPTRQ(a->rowners);
  PLogObjectMemory(mat,(a->size+2)*sizeof(int)+sizeof(struct _Mat)+
                       sizeof(Mat_MPIDense));
  MPI_Allgather(&m,1,MPI_INT,a->rowners+1,1,MPI_INT,comm);
  a->rowners[0] = 0;
  for ( i=2; i<=a->size; i++ ) {
    a->rowners[i] += a->rowners[i-1];
  }
  a->rstart = a->rowners[a->rank];
  a->rend   = a->rowners[a->rank+1];

  ierr = MatCreateSeqDense(MPI_COMM_SELF,m,N,&a->A); CHKERRQ(ierr);
  PLogObjectParent(mat,a->A);

  /* build cache for off array entries formed */
  ierr = StashBuild_Private(&a->stash); CHKERRQ(ierr);

  /* stuff used for matrix vector multiply */
  a->lvec      = 0;
  a->Mvctx     = 0;
  a->assembled = 0;

  *newmat = mat;
  return 0;
}

static int MatCopyPrivate_MPIDense(Mat matin,Mat *newmat)
{
  Mat        mat;
  Mat_MPIDense *a,*oldmat = (Mat_MPIDense *) matin->data;
  int        ierr;

  if (!oldmat->assembled) SETERRQ(1,"MatCopyPrivate_MPIDense:Must assemble matrix");
  *newmat       = 0;
  PETSCHEADERCREATE(mat,_Mat,MAT_COOKIE,MATMPIDENSE,matin->comm);
  PLogObjectCreate(mat);
  mat->data     = (void *) (a = PETSCNEW(Mat_MPIDense)); CHKPTRQ(a);
  PetscMemcpy(&mat->ops,&MatOps,sizeof(struct _MatOps));
  mat->destroy  = MatDestroy_MPIDense;
  mat->view     = MatView_MPIDense;
  mat->factor   = matin->factor;

  a->m          = oldmat->m;
  a->n          = oldmat->n;
  a->M          = oldmat->M;
  a->N          = oldmat->N;

  a->assembled  = 1;
  a->rstart     = oldmat->rstart;
  a->rend       = oldmat->rend;
  a->size       = oldmat->size;
  a->rank       = oldmat->rank;
  a->insertmode = NOT_SET_VALUES;

  a->rowners = (int *) PETSCMALLOC((a->size+1)*sizeof(int)); CHKPTRQ(a->rowners);
  PLogObjectMemory(mat,(a->size+1)*sizeof(int)+sizeof(struct _Mat)+sizeof(Mat_MPIDense));
  PetscMemcpy(a->rowners,oldmat->rowners,(a->size+1)*sizeof(int));
  ierr = StashInitialize_Private(&a->stash); CHKERRQ(ierr);

  ierr =  VecDuplicate(oldmat->lvec,&a->lvec); CHKERRQ(ierr);
  PLogObjectParent(mat,a->lvec);
  ierr =  VecScatterCtxCopy(oldmat->Mvctx,&a->Mvctx); CHKERRQ(ierr);
  PLogObjectParent(mat,a->Mvctx);
  ierr =  MatConvert(oldmat->A,MATSAME,&a->A); CHKERRQ(ierr);
  PLogObjectParent(mat,a->A);
  *newmat = mat;
  return 0;
}

#include "sysio.h"

int MatLoad_MPIDense(Viewer bview,MatType type,Mat *newmat)
{
  Mat          A;
  int          i, nz, ierr, j,rstart, rend, fd;
  Scalar       *vals,*svals;
  PetscObject  vobj = (PetscObject) bview;
  MPI_Comm     comm = vobj->comm;
  MPI_Status   status;
  int          header[4],rank,size,*rowlengths = 0,M,N,m,*rowners,maxnz,*cols;
  int          *ourlens,*sndcounts = 0,*procsnz = 0, *offlens,jj,*mycols,*smycols;
  int          tag = ((PetscObject)bview)->tag;

  MPI_Comm_size(comm,&size); MPI_Comm_rank(comm,&rank);
  if (!rank) {
    ierr = ViewerFileGetDescriptor_Private(bview,&fd); CHKERRQ(ierr);
    ierr = SYRead(fd,(char *)header,4,SYINT); CHKERRQ(ierr);
    if (header[0] != MAT_COOKIE) SETERRQ(1,"MatLoad_MPIDenseorMPIRow:not matrix object");
  }

  MPI_Bcast(header+1,3,MPI_INT,0,comm);
  M = header[1]; N = header[2];
  /* determine ownership of all rows */
  m = M/size + ((M % size) > rank);
  rowners = (int *) PETSCMALLOC((size+2)*sizeof(int)); CHKPTRQ(rowners);
  MPI_Allgather(&m,1,MPI_INT,rowners+1,1,MPI_INT,comm);
  rowners[0] = 0;
  for ( i=2; i<=size; i++ ) {
    rowners[i] += rowners[i-1];
  }
  rstart = rowners[rank];
  rend   = rowners[rank+1];

  /* distribute row lengths to all processors */
  ourlens = (int*) PETSCMALLOC( 2*(rend-rstart)*sizeof(int) ); CHKPTRQ(ourlens);
  offlens = ourlens + (rend-rstart);
  if (!rank) {
    rowlengths = (int*) PETSCMALLOC( M*sizeof(int) ); CHKPTRQ(rowlengths);
    ierr = SYRead(fd,rowlengths,M,SYINT); CHKERRQ(ierr);
    sndcounts = (int*) PETSCMALLOC( size*sizeof(int) ); CHKPTRQ(sndcounts);
    for ( i=0; i<size; i++ ) sndcounts[i] = rowners[i+1] - rowners[i];
    MPI_Scatterv(rowlengths,sndcounts,rowners,MPI_INT,ourlens,rend-rstart,MPI_INT,0,comm);
    PETSCFREE(sndcounts);
  }
  else {
    MPI_Scatterv(0,0,0,MPI_INT,ourlens,rend-rstart,MPI_INT, 0,comm);
  }

  if (!rank) {
    /* calculate the number of nonzeros on each processor */
    procsnz = (int*) PETSCMALLOC( size*sizeof(int) ); CHKPTRQ(procsnz);
    PetscZero(procsnz,size*sizeof(int));
    for ( i=0; i<size; i++ ) {
      for ( j=rowners[i]; j< rowners[i+1]; j++ ) {
        procsnz[i] += rowlengths[j];
      }
    }
    PETSCFREE(rowlengths);

    /* determine max buffer needed and allocate it */
    maxnz = 0;
    for ( i=0; i<size; i++ ) {
      maxnz = PETSCMAX(maxnz,procsnz[i]);
    }
    cols = (int *) PETSCMALLOC( maxnz*sizeof(int) ); CHKPTRQ(cols);

    /* read in my part of the matrix column indices  */
    nz = procsnz[0];
    mycols = (int *) PETSCMALLOC( nz*sizeof(int) ); CHKPTRQ(mycols);
    ierr = SYRead(fd,mycols,nz,SYINT); CHKERRQ(ierr);

    /* read in every one elses and ship off */
    for ( i=1; i<size; i++ ) {
      nz = procsnz[i];
      ierr = SYRead(fd,cols,nz,SYINT); CHKERRQ(ierr);
      MPI_Send(cols,nz,MPI_INT,i,tag,comm);
    }
    PETSCFREE(cols);
  }
  else {
    /* determine buffer space needed for message */
    nz = 0;
    for ( i=0; i<m; i++ ) {
      nz += ourlens[i];
    }
    mycols = (int*) PETSCMALLOC( nz*sizeof(int) ); CHKPTRQ(mycols);

    /* receive message of column indices*/
    MPI_Recv(mycols,nz,MPI_INT,0,tag,comm,&status);
    MPI_Get_count(&status,MPI_INT,&maxnz);
    if (maxnz != nz) SETERRQ(1,"MatLoad_MPIDenseorMPIRow:something is wrong with file");
  }

  /* loop over local rows, determining number of off diagonal entries */
  PetscZero(offlens,m*sizeof(int));
  jj = 0;
  for ( i=0; i<m; i++ ) {
    for ( j=0; j<ourlens[i]; j++ ) {
      if (mycols[jj] < rstart || mycols[jj] >= rend) offlens[i]++;
      jj++;
    }
  }

  /* create our matrix */
  for ( i=0; i<m; i++ ) {
    ourlens[i] -= offlens[i];
  }
  if (type == MATMPIDENSE) {
    ierr = MatCreateMPIDense(comm,m,PETSC_DECIDE,M,N,newmat);CHKERRQ(ierr);
  }
  A = *newmat;
  MatSetOption(A,COLUMNS_SORTED);
  for ( i=0; i<m; i++ ) {
    ourlens[i] += offlens[i];
  }

  if (!rank) {
    vals = (Scalar *) PETSCMALLOC( maxnz*sizeof(Scalar) ); CHKPTRQ(vals);

    /* read in my part of the matrix numerical values  */
    nz = procsnz[0];
    ierr = SYRead(fd,vals,nz,SYSCALAR); CHKERRQ(ierr);

    /* insert into matrix */
    jj      = rstart;
    smycols = mycols;
    svals   = vals;
    for ( i=0; i<m; i++ ) {
      ierr = MatSetValues(A,1,&jj,ourlens[i],smycols,svals,INSERT_VALUES);CHKERRQ(ierr);
      smycols += ourlens[i];
      svals   += ourlens[i];
      jj++;
    }

    /* read in other processors and ship out */
    for ( i=1; i<size; i++ ) {
      nz = procsnz[i];
      ierr = SYRead(fd,vals,nz,SYSCALAR); CHKERRQ(ierr);
      MPI_Send(vals,nz,MPIU_SCALAR,i,A->tag,comm);
    }
    PETSCFREE(procsnz);
  }
  else {
    /* receive numeric values */
    vals = (Scalar*) PETSCMALLOC( nz*sizeof(Scalar) ); CHKPTRQ(vals);

    /* receive message of values*/
    MPI_Recv(vals,nz,MPIU_SCALAR,0,A->tag,comm,&status);
    MPI_Get_count(&status,MPIU_SCALAR,&maxnz);
    if (maxnz != nz) SETERRQ(1,"MatLoad_MPIDenseorMPIRow:something is wrong with file");

    /* insert into matrix */
    jj      = rstart;
    smycols = mycols;
    svals   = vals;
    for ( i=0; i<m; i++ ) {
      ierr = MatSetValues(A,1,&jj,ourlens[i],smycols,svals,INSERT_VALUES);CHKERRQ(ierr);
      smycols += ourlens[i];
      svals   += ourlens[i];
      jj++;
    }
  }
  PETSCFREE(ourlens); PETSCFREE(vals); PETSCFREE(mycols); PETSCFREE(rowners);

  ierr = MatAssemblyBegin(A,FINAL_ASSEMBLY); CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,FINAL_ASSEMBLY); CHKERRQ(ierr);
  return 0;
}