xref: /petsc/src/ksp/pc/impls/tfs/xxt.c (revision db4deed73f06ae556a0f2e02a0fd6e016e156849)

/*************************************xxt.c************************************
Module Name: xxt
Module Info:

author:  Henry M. Tufo III
e-mail:  hmt@asci.uchicago.edu
contact:
+--------------------------------+--------------------------------+
|MCS Division - Building 221     |Department of Computer Science  |
|Argonne National Laboratory     |Ryerson 152                     |
|9700 S. Cass Avenue             |The University of Chicago       |
|Argonne, IL  60439              |Chicago, IL  60637              |
|(630) 252-5354/5986 ph/fx       |(773) 702-6019/8487 ph/fx       |
+--------------------------------+--------------------------------+

Last Modification: 3.20.01
**************************************xxt.c***********************************/
#include <../src/ksp/pc/impls/tfs/tfs.h>

#define LEFT  -1
#define RIGHT  1
#define BOTH   0

typedef struct xxt_solver_info {
  PetscInt n, m, n_global, m_global;
  PetscInt nnz, max_nnz, msg_buf_sz;
  PetscInt *nsep, *lnsep, *fo, nfo, *stages;
  PetscInt *col_sz, *col_indices;
  PetscScalar **col_vals, *x, *solve_uu, *solve_w;
  PetscInt nsolves;
  PetscScalar tot_solve_time;
} xxt_info;

typedef struct matvec_info {
  PetscInt n, m, n_global, m_global;
  PetscInt *local2global;
  PCTFS_gs_ADT PCTFS_gs_handle;
  PetscErrorCode (*matvec)(struct matvec_info*,PetscScalar*,PetscScalar*);
  void *grid_data;
} mv_info;

struct xxt_CDT{
  PetscInt id;
  PetscInt ns;
  PetscInt level;
  xxt_info *info;
  mv_info  *mvi;
};

static PetscInt n_xxt=0;
static PetscInt n_xxt_handles=0;

/* prototypes */
static PetscErrorCode do_xxt_solve(xxt_ADT xxt_handle, PetscScalar *rhs);
static PetscErrorCode check_handle(xxt_ADT xxt_handle);
static PetscErrorCode det_separators(xxt_ADT xxt_handle);
static PetscErrorCode do_matvec(mv_info *A, PetscScalar *v, PetscScalar *u);
static PetscInt xxt_generate(xxt_ADT xxt_handle);
static PetscInt do_xxt_factor(xxt_ADT xxt_handle);
static mv_info *set_mvi(PetscInt *local2global, PetscInt n, PetscInt m, void *matvec, void *grid_data);

/**************************************xxt.c***********************************/
xxt_ADT XXT_new(void)
{
  xxt_ADT xxt_handle;

  /* rolling count on n_xxt ... pot. problem here */
  n_xxt_handles++;
  xxt_handle       = (xxt_ADT)malloc(sizeof(struct xxt_CDT));
  xxt_handle->id   = ++n_xxt;
  xxt_handle->info = NULL; xxt_handle->mvi  = NULL;

  return(xxt_handle);
}

/**************************************xxt.c***********************************/
PetscInt XXT_factor(xxt_ADT xxt_handle, /* prev. allocated xxt  handle */
           PetscInt *local2global,  /* global column mapping       */
           PetscInt n,              /* local num rows              */
           PetscInt m,              /* local num cols              */
           void *matvec,       /* b_loc=A_local.x_loc         */
           void *grid_data     /* grid data for matvec        */
           )
{
  PCTFS_comm_init();
  check_handle(xxt_handle);

  /* only 2^k for now and all nodes participating */
  if ((1<<(xxt_handle->level=PCTFS_i_log2_num_nodes))!=PCTFS_num_nodes) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_PLIB,"only 2^k for now and MPI_COMM_WORLD!!! %D != %D\n",1<<PCTFS_i_log2_num_nodes,PCTFS_num_nodes);

  /* space for X info */
  xxt_handle->info = (xxt_info*)malloc(sizeof(xxt_info));

  /* set up matvec handles */
  xxt_handle->mvi  = set_mvi(local2global, n, m, matvec, grid_data);

  /* matrix is assumed to be of full rank */
  /* LATER we can reset to indicate rank def. */
  xxt_handle->ns=0;

  /* determine separators and generate firing order - NB xxt info set here */
  det_separators(xxt_handle);

  return(do_xxt_factor(xxt_handle));
}

/**************************************xxt.c***********************************/
PetscInt XXT_solve(xxt_ADT xxt_handle, PetscScalar *x, PetscScalar *b)
{

  PCTFS_comm_init();
  check_handle(xxt_handle);

  /* need to copy b into x? */
  if (b) {PCTFS_rvec_copy(x,b,xxt_handle->mvi->n);}
  do_xxt_solve(xxt_handle,x);

  return(0);
}

/**************************************xxt.c***********************************/
PetscInt XXT_free(xxt_ADT xxt_handle)
{

  PCTFS_comm_init();
  check_handle(xxt_handle);
  n_xxt_handles--;

  free(xxt_handle->info->nsep);
  free(xxt_handle->info->lnsep);
  free(xxt_handle->info->fo);
  free(xxt_handle->info->stages);
  free(xxt_handle->info->solve_uu);
  free(xxt_handle->info->solve_w);
  free(xxt_handle->info->x);
  free(xxt_handle->info->col_vals);
  free(xxt_handle->info->col_sz);
  free(xxt_handle->info->col_indices);
  free(xxt_handle->info);
  free(xxt_handle->mvi->local2global);
   PCTFS_gs_free(xxt_handle->mvi->PCTFS_gs_handle);
  free(xxt_handle->mvi);
  free(xxt_handle);

  /* if the check fails we nuke */
  /* if NULL pointer passed to free we nuke */
  /* if the calls to free fail that's not my problem */
  return(0);
}

/**************************************xxt.c***********************************/
PetscInt XXT_stats(xxt_ADT xxt_handle)
{
  PetscInt       op[] = {NON_UNIFORM,GL_MIN,GL_MAX,GL_ADD,GL_MIN,GL_MAX,GL_ADD,GL_MIN,GL_MAX,GL_ADD};
  PetscInt       fop[] = {NON_UNIFORM,GL_MIN,GL_MAX,GL_ADD};
  PetscInt       vals[9],  work[9];
  PetscScalar    fvals[3], fwork[3];
  PetscErrorCode ierr;

  PCTFS_comm_init();
  check_handle(xxt_handle);

  /* if factorization not done there are no stats */
  if (!xxt_handle->info||!xxt_handle->mvi) {
    if (!PCTFS_my_id) { ierr = PetscPrintf(PETSC_COMM_WORLD,"XXT_stats() :: no stats available!\n");CHKERRQ(ierr); }
    return 1;
  }

  vals[0]=vals[1]=vals[2]=xxt_handle->info->nnz;
  vals[3]=vals[4]=vals[5]=xxt_handle->mvi->n;
  vals[6]=vals[7]=vals[8]=xxt_handle->info->msg_buf_sz;
  PCTFS_giop(vals,work,sizeof(op)/sizeof(op[0])-1,op);

  fvals[0]=fvals[1]=fvals[2]
    =xxt_handle->info->tot_solve_time/xxt_handle->info->nsolves++;
  PCTFS_grop(fvals,fwork,sizeof(fop)/sizeof(fop[0])-1,fop);

  if (!PCTFS_my_id) {
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: min   xxt_nnz=%D\n",PCTFS_my_id,vals[0]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: max   xxt_nnz=%D\n",PCTFS_my_id,vals[1]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: avg   xxt_nnz=%g\n",PCTFS_my_id,1.0*vals[2]/PCTFS_num_nodes);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: tot   xxt_nnz=%D\n",PCTFS_my_id,vals[2]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: xxt   C(2d)  =%g\n",PCTFS_my_id,vals[2]/(pow(1.0*vals[5],1.5)));CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: xxt   C(3d)  =%g\n",PCTFS_my_id,vals[2]/(pow(1.0*vals[5],1.6667)));CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: min   xxt_n  =%D\n",PCTFS_my_id,vals[3]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: max   xxt_n  =%D\n",PCTFS_my_id,vals[4]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: avg   xxt_n  =%g\n",PCTFS_my_id,1.0*vals[5]/PCTFS_num_nodes);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: tot   xxt_n  =%D\n",PCTFS_my_id,vals[5]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: min   xxt_buf=%D\n",PCTFS_my_id,vals[6]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: max   xxt_buf=%D\n",PCTFS_my_id,vals[7]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: avg   xxt_buf=%g\n",PCTFS_my_id,1.0*vals[8]/PCTFS_num_nodes);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: min   xxt_slv=%g\n",PCTFS_my_id,fvals[0]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: max   xxt_slv=%g\n",PCTFS_my_id,fvals[1]);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD,"%D :: avg   xxt_slv=%g\n",PCTFS_my_id,fvals[2]/PCTFS_num_nodes);CHKERRQ(ierr);
  }

  return(0);
}

/*************************************xxt.c************************************

Description: get A_local, local portion of global coarse matrix which
is a row dist. nxm matrix w/ n<m.
   o my_ml holds address of ML struct associated w/A_local and coarse grid
   o local2global holds global number of column i (i=0,...,m-1)
   o local2global holds global number of row    i (i=0,...,n-1)
   o mylocmatvec performs A_local . vec_local (note that gs is performed using
   PCTFS_gs_init/gop).

mylocmatvec = my_ml->Amat[grid_tag].matvec->external;
mylocmatvec (void :: void *data, double *in, double *out)
**************************************xxt.c***********************************/
static PetscInt do_xxt_factor(xxt_ADT xxt_handle)
{
  return xxt_generate(xxt_handle);
}

/**************************************xxt.c***********************************/
static PetscInt xxt_generate(xxt_ADT xxt_handle)
{
  PetscInt i,j,k,idex;
  PetscInt dim, col;
  PetscScalar *u, *uu, *v, *z, *w, alpha, alpha_w;
  PetscInt *segs;
  PetscInt op[] = {GL_ADD,0};
  PetscInt off, len;
  PetscScalar *x_ptr;
  PetscInt *iptr, flag;
  PetscInt start=0, end, work;
  PetscInt op2[] = {GL_MIN,0};
  PCTFS_gs_ADT PCTFS_gs_handle;
  PetscInt *nsep, *lnsep, *fo;
  PetscInt a_n=xxt_handle->mvi->n;
  PetscInt a_m=xxt_handle->mvi->m;
  PetscInt *a_local2global=xxt_handle->mvi->local2global;
  PetscInt level;
  PetscInt xxt_nnz=0, xxt_max_nnz=0;
  PetscInt n, m;
  PetscInt *col_sz, *col_indices, *stages;
  PetscScalar **col_vals, *x;
  PetscInt n_global;
  PetscInt xxt_zero_nnz=0;
  PetscInt xxt_zero_nnz_0=0;
  PetscBLASInt i1 = 1,dlen;
  PetscScalar dm1 = -1.0;
  PetscErrorCode ierr;

  n=xxt_handle->mvi->n;
  nsep=xxt_handle->info->nsep;
  lnsep=xxt_handle->info->lnsep;
  fo=xxt_handle->info->fo;
  end=lnsep[0];
  level=xxt_handle->level;
  PCTFS_gs_handle=xxt_handle->mvi->PCTFS_gs_handle;

  /* is there a null space? */
  /* LATER add in ability to detect null space by checking alpha */
  for (i=0, j=0; i<=level; i++)
    {j+=nsep[i];}

  m = j-xxt_handle->ns;
  if (m!=j) {
    ierr = PetscPrintf(PETSC_COMM_WORLD,"xxt_generate() :: null space exists %D %D %D\n",m,j,xxt_handle->ns);CHKERRQ(ierr);
  }

  /* get and initialize storage for x local         */
  /* note that x local is nxm and stored by columns */
  col_sz = (PetscInt*) malloc(m*sizeof(PetscInt));
  col_indices = (PetscInt*) malloc((2*m+1)*sizeof(PetscInt));
  col_vals = (PetscScalar **) malloc(m*sizeof(PetscScalar *));
  for (i=j=0; i<m; i++, j+=2) {
    col_indices[j]=col_indices[j+1]=col_sz[i]=-1;
    col_vals[i] = NULL;
  }
  col_indices[j]=-1;

  /* size of separators for each sub-hc working from bottom of tree to top */
  /* this looks like nsep[]=segments */
  stages = (PetscInt*) malloc((level+1)*sizeof(PetscInt));
  segs   = (PetscInt*) malloc((level+1)*sizeof(PetscInt));
  PCTFS_ivec_zero(stages,level+1);
  PCTFS_ivec_copy(segs,nsep,level+1);
  for (i=0; i<level; i++) { segs[i+1] += segs[i]; }
  stages[0] = segs[0];

  /* temporary vectors  */
  u  = (PetscScalar *) malloc(n*sizeof(PetscScalar));
  z  = (PetscScalar *) malloc(n*sizeof(PetscScalar));
  v  = (PetscScalar *) malloc(a_m*sizeof(PetscScalar));
  uu = (PetscScalar *) malloc(m*sizeof(PetscScalar));
  w  = (PetscScalar *) malloc(m*sizeof(PetscScalar));

  /* extra nnz due to replication of vertices across separators */
  for (i=1, j=0; i<=level; i++) {j+=nsep[i];}

  /* storage for sparse x values */
  n_global = xxt_handle->info->n_global;
  xxt_max_nnz = (PetscInt)(2.5*pow(1.0*n_global,1.6667) + j*n/2)/PCTFS_num_nodes;
  x = (PetscScalar *) malloc(xxt_max_nnz*sizeof(PetscScalar));
  xxt_nnz = 0;

  /* LATER - can embed next sep to fire in gs */
  /* time to make the donuts - generate X factor */
  for (dim=i=j=0;i<m;i++)
  {
    /* time to move to the next level? */
    while (i==segs[dim]) {
      if (dim==level) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"dim about to exceed level\n");
      stages[dim++]=i;
      end+=lnsep[dim];
    }
    stages[dim]=i;

    /* which column are we firing? */
    /* i.e. set v_l */
    /* use new seps and do global min across hc to determine which one to fire */
    (start<end) ? (col=fo[start]) : (col=INT_MAX);
    PCTFS_giop_hc(&col,&work,1,op2,dim);

    /* shouldn't need this */
    if (col==INT_MAX) {
      ierr = PetscInfo(0,"hey ... col==INT_MAX??\n");CHKERRQ(ierr);
      continue;
    }

    /* do I own it? I should */
    PCTFS_rvec_zero(v ,a_m);
    if (col==fo[start]) {
      start++;
      idex=PCTFS_ivec_linear_search(col, a_local2global, a_n);
      if (idex!=-1) {
        v[idex] = 1.0; j++;
      } else SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"NOT FOUND!\n");
    } else {
      idex=PCTFS_ivec_linear_search(col, a_local2global, a_m);
      if (idex!=-1)
        {v[idex] = 1.0;}
    }

    /* perform u = A.v_l */
    PCTFS_rvec_zero(u,n);
    do_matvec(xxt_handle->mvi,v,u);

    /* uu =  X^T.u_l (local portion) */
    /* technically only need to zero out first i entries */
    /* later turn this into an XXT_solve call ? */
    PCTFS_rvec_zero(uu,m);
    x_ptr=x;
    iptr = col_indices;
    for (k=0; k<i; k++) {
      off = *iptr++;
      len = *iptr++;
      dlen = PetscBLASIntCast(len);
      uu[k] = BLASdot_(&dlen,u+off,&i1,x_ptr,&i1);
      x_ptr+=len;
    }


    /* uu = X^T.u_l (comm portion) */
    PCTFS_ssgl_radd  (uu, w, dim, stages);

    /* z = X.uu */
    PCTFS_rvec_zero(z,n);
    x_ptr=x;
    iptr = col_indices;
    for (k=0; k<i; k++) {
      off = *iptr++;
      len = *iptr++;
      dlen = PetscBLASIntCast(len);
      BLASaxpy_(&dlen,&uu[k],x_ptr,&i1,z+off,&i1);
      x_ptr+=len;
    }

    /* compute v_l = v_l - z */
    PCTFS_rvec_zero(v+a_n,a_m-a_n);
    dlen = PetscBLASIntCast(n);
    BLASaxpy_(&dlen,&dm1,z,&i1,v,&i1);

    /* compute u_l = A.v_l */
    if (a_n!=a_m) { PCTFS_gs_gop_hc(PCTFS_gs_handle,v,"+\0",dim); }
    PCTFS_rvec_zero(u,n);
    do_matvec(xxt_handle->mvi,v,u);

    /* compute sqrt(alpha) = sqrt(v_l^T.u_l) - local portion */
    dlen = PetscBLASIntCast(n);
    alpha = BLASdot_(&dlen,u,&i1,v,&i1);
    /* compute sqrt(alpha) = sqrt(v_l^T.u_l) - comm portion */
    PCTFS_grop_hc(&alpha, &alpha_w, 1, op, dim);

    alpha = (PetscScalar) PetscSqrtReal((PetscReal)alpha);

    /* check for small alpha                             */
    /* LATER use this to detect and determine null space */
    if (fabs(alpha)<1.0e-14) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_PLIB,"bad alpha! %g\n",alpha);

    /* compute v_l = v_l/sqrt(alpha) */
    PCTFS_rvec_scale(v,1.0/alpha,n);

    /* add newly generated column, v_l, to X */
    flag = 1;
    off=len=0;
    for (k=0; k<n; k++) {
      if (v[k]!=0.0) {
        len=k;
        if (flag) { off=k; flag=0; }
      }
    }

    len -= (off-1);

    if (len>0) {
      if ((xxt_nnz+len)>xxt_max_nnz) {
        ierr = PetscInfo(0,"increasing space for X by 2x!\n");CHKERRQ(ierr);
        xxt_max_nnz *= 2;
        x_ptr = (PetscScalar *) malloc(xxt_max_nnz*sizeof(PetscScalar));
        PCTFS_rvec_copy(x_ptr,x,xxt_nnz);
        free(x);
        x = x_ptr;
        x_ptr+=xxt_nnz;
      }
      xxt_nnz += len;
      PCTFS_rvec_copy(x_ptr,v+off,len);

      /* keep track of number of zeros */
      if (dim) {
        for (k=0; k<len; k++) {
          if (x_ptr[k]==0.0) { xxt_zero_nnz++; }
        }
      } else {
        for (k=0; k<len; k++) {
          if (x_ptr[k]==0.0) {xxt_zero_nnz_0++;}
        }
      }
      col_indices[2*i] = off;
      col_sz[i] = col_indices[2*i+1] = len;
      col_vals[i] = x_ptr;
    }
    else {
      col_indices[2*i] = 0;
      col_sz[i] = col_indices[2*i+1] = 0;
      col_vals[i] = x_ptr;
    }
  }

  /* close off stages for execution phase */
  while (dim!=level) {
    stages[dim++]=i;
    ierr = PetscInfo2(0,"disconnected!!! dim(%D)!=level(%D)\n",dim,level);CHKERRQ(ierr);
  }
  stages[dim]=i;

  xxt_handle->info->n=xxt_handle->mvi->n;
  xxt_handle->info->m=m;
  xxt_handle->info->nnz=xxt_nnz;
  xxt_handle->info->max_nnz=xxt_max_nnz;
  xxt_handle->info->msg_buf_sz=stages[level]-stages[0];
  xxt_handle->info->solve_uu = (PetscScalar *) malloc(m*sizeof(PetscScalar));
  xxt_handle->info->solve_w  = (PetscScalar *) malloc(m*sizeof(PetscScalar));
  xxt_handle->info->x=x;
  xxt_handle->info->col_vals=col_vals;
  xxt_handle->info->col_sz=col_sz;
  xxt_handle->info->col_indices=col_indices;
  xxt_handle->info->stages=stages;
  xxt_handle->info->nsolves=0;
  xxt_handle->info->tot_solve_time=0.0;

  free(segs);
  free(u);
  free(v);
  free(uu);
  free(z);
  free(w);

  return(0);
}

/**************************************xxt.c***********************************/
static PetscErrorCode do_xxt_solve(xxt_ADT xxt_handle,  PetscScalar *uc)
{
  PetscInt off, len, *iptr;
  PetscInt level       =xxt_handle->level;
  PetscInt n           =xxt_handle->info->n;
  PetscInt m           =xxt_handle->info->m;
  PetscInt *stages     =xxt_handle->info->stages;
  PetscInt *col_indices=xxt_handle->info->col_indices;
  PetscScalar *x_ptr, *uu_ptr;
  PetscScalar *solve_uu=xxt_handle->info->solve_uu;
  PetscScalar *solve_w =xxt_handle->info->solve_w;
  PetscScalar *x       =xxt_handle->info->x;
  PetscBLASInt i1 = 1,dlen;

  PetscFunctionBegin;
  uu_ptr=solve_uu;
  PCTFS_rvec_zero(uu_ptr,m);

  /* x  = X.Y^T.b */
  /* uu = Y^T.b */
  for (x_ptr=x,iptr=col_indices; *iptr!=-1; x_ptr+=len) {
    off=*iptr++; len=*iptr++;
    dlen = PetscBLASIntCast(len);
    *uu_ptr++ = BLASdot_(&dlen,uc+off,&i1,x_ptr,&i1);
  }

  /* comunication of beta */
  uu_ptr=solve_uu;
  if (level) { PCTFS_ssgl_radd(uu_ptr, solve_w, level, stages); }

  PCTFS_rvec_zero(uc,n);

  /* x = X.uu */
  for (x_ptr=x,iptr=col_indices; *iptr!=-1; x_ptr+=len) {
    off=*iptr++; len=*iptr++;
    dlen = PetscBLASIntCast(len);
    BLASaxpy_(&dlen,uu_ptr++,x_ptr,&i1,uc+off,&i1);
  }
  PetscFunctionReturn(0);
}

/**************************************xxt.c***********************************/
static PetscErrorCode check_handle(xxt_ADT xxt_handle)
{
  PetscInt vals[2], work[2], op[] = {NON_UNIFORM,GL_MIN,GL_MAX};

  PetscFunctionBegin;
  if (!xxt_handle) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_PLIB,"check_handle() :: bad handle :: NULL %D\n",xxt_handle);

  vals[0]=vals[1]=xxt_handle->id;
  PCTFS_giop(vals,work,sizeof(op)/sizeof(op[0])-1,op);
  if ((vals[0]!=vals[1])||(xxt_handle->id<=0)) SETERRQ3(PETSC_COMM_SELF,PETSC_ERR_PLIB,"check_handle() :: bad handle :: id mismatch min/max %D/%D %D\n",vals[0],vals[1], xxt_handle->id);
  PetscFunctionReturn(0);
}

/**************************************xxt.c***********************************/
static  PetscErrorCode det_separators(xxt_ADT xxt_handle)
{
  PetscInt i, ct, id;
  PetscInt mask, edge, *iptr;
  PetscInt *dir, *used;
  PetscInt sum[4], w[4];
  PetscScalar rsum[4], rw[4];
  PetscInt op[] = {GL_ADD,0};
  PetscScalar *lhs, *rhs;
  PetscInt *nsep, *lnsep, *fo, nfo=0;
  PCTFS_gs_ADT PCTFS_gs_handle=xxt_handle->mvi->PCTFS_gs_handle;
  PetscInt *local2global=xxt_handle->mvi->local2global;
  PetscInt  n=xxt_handle->mvi->n;
  PetscInt  m=xxt_handle->mvi->m;
  PetscInt level=xxt_handle->level;
  PetscInt shared=0;

  PetscFunctionBegin;
  dir  = (PetscInt*)malloc(sizeof(PetscInt)*(level+1));
  nsep = (PetscInt*)malloc(sizeof(PetscInt)*(level+1));
  lnsep= (PetscInt*)malloc(sizeof(PetscInt)*(level+1));
  fo   = (PetscInt*)malloc(sizeof(PetscInt)*(n+1));
  used = (PetscInt*)malloc(sizeof(PetscInt)*n);

  PCTFS_ivec_zero(dir  ,level+1);
  PCTFS_ivec_zero(nsep ,level+1);
  PCTFS_ivec_zero(lnsep,level+1);
  PCTFS_ivec_set (fo   ,-1,n+1);
  PCTFS_ivec_zero(used,n);

  lhs  = (PetscScalar*)malloc(sizeof(PetscScalar)*m);
  rhs  = (PetscScalar*)malloc(sizeof(PetscScalar)*m);

  /* determine the # of unique dof */
  PCTFS_rvec_zero(lhs,m);
  PCTFS_rvec_set(lhs,1.0,n);
  PCTFS_gs_gop_hc(PCTFS_gs_handle,lhs,"+\0",level);
  PCTFS_rvec_zero(rsum,2);
  for (ct=i=0;i<n;i++) {
    if (lhs[i]!=0.0)
      {rsum[0]+=1.0/lhs[i]; rsum[1]+=lhs[i];}
  }
  PCTFS_grop_hc(rsum,rw,2,op,level);
  rsum[0]+=0.1;
  rsum[1]+=0.1;

  if (fabs(rsum[0]-rsum[1])>EPS) { shared=1; }

  xxt_handle->info->n_global=xxt_handle->info->m_global=(PetscInt) rsum[0];
  xxt_handle->mvi->n_global =xxt_handle->mvi->m_global =(PetscInt) rsum[0];

  /* determine separator sets top down */
  if (shared)
  {
    for (iptr=fo+n,id=PCTFS_my_id,mask=PCTFS_num_nodes>>1,edge=level;edge>0;edge--,mask>>=1) {

      /* set rsh of hc, fire, and collect lhs responses */
      (id<mask) ? PCTFS_rvec_zero(lhs,m) : PCTFS_rvec_set(lhs,1.0,m);
      PCTFS_gs_gop_hc(PCTFS_gs_handle,lhs,"+\0",edge);

      /* set lsh of hc, fire, and collect rhs responses */
      (id<mask) ? PCTFS_rvec_set(rhs,1.0,m) : PCTFS_rvec_zero(rhs,m);
      PCTFS_gs_gop_hc(PCTFS_gs_handle,rhs,"+\0",edge);

      for (i=0;i<n;i++) {
        if (id< mask) {
          if (lhs[i]!=0.0) { lhs[i]=1.0; }
        }

        if (id>=mask) {
          if (rhs[i]!=0.0) { rhs[i]=1.0; }
        }
      }

      if (id< mask) { PCTFS_gs_gop_hc(PCTFS_gs_handle,lhs,"+\0",edge-1); }
      else          { PCTFS_gs_gop_hc(PCTFS_gs_handle,rhs,"+\0",edge-1); }

      /* count number of dofs I own that have signal and not in sep set */
      PCTFS_rvec_zero(rsum,4);
      for (PCTFS_ivec_zero(sum,4),ct=i=0;i<n;i++) {

        if (!used[i]) {
          /* number of unmarked dofs on node */
          ct++;
          /* number of dofs to be marked on lhs hc */
          if (id< mask) {
            if (lhs[i]!=0.0) { sum[0]++; rsum[0]+=1.0/lhs[i]; }
          }
          /* number of dofs to be marked on rhs hc */
          if (id>=mask) {
            if (rhs[i]!=0.0) { sum[1]++; rsum[1]+=1.0/rhs[i]; }
          }
        }

      }

      /* go for load balance - choose half with most unmarked dofs, bias LHS */
      (id<mask) ? (sum[2]=ct) : (sum[3]=ct);
      (id<mask) ? (rsum[2]=ct) : (rsum[3]=ct);
      PCTFS_giop_hc(sum,w,4,op,edge);
      PCTFS_grop_hc(rsum,rw,4,op,edge);
      rsum[0]+=0.1; rsum[1]+=0.1; rsum[2]+=0.1; rsum[3]+=0.1;

      if (id<mask) {
        /* mark dofs I own that have signal and not in sep set */
        for (ct=i=0;i<n;i++) {
          if ((!used[i])&&(lhs[i]!=0.0)) {
            ct++; nfo++;

            if (nfo>n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"nfo about to exceed n\n");

            *--iptr = local2global[i];
            used[i]=edge;
          }
        }
        if (ct>1) {PCTFS_ivec_sort(iptr,ct);}

        lnsep[edge]=ct;
        nsep[edge]=(PetscInt) rsum[0];
        dir [edge]=LEFT;
      }

      if (id>=mask) {
        /* mark dofs I own that have signal and not in sep set */
        for (ct=i=0;i<n;i++) {
          if ((!used[i])&&(rhs[i]!=0.0)) {
            ct++; nfo++;

            if (nfo>n) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"nfo about to exceed n\n");

            *--iptr = local2global[i];
            used[i]=edge;
          }
        }
        if (ct>1) { PCTFS_ivec_sort(iptr,ct); }

        lnsep[edge]=ct;
        nsep[edge]= (PetscInt) rsum[1];
        dir [edge]=RIGHT;
      }

      /* LATER or we can recur on these to order seps at this level */
      /* do we need full set of separators for this?                */

      /* fold rhs hc into lower */
      if (id>=mask) { id-=mask; }
    }
  } else {
    for (iptr=fo+n,id=PCTFS_my_id,mask=PCTFS_num_nodes>>1,edge=level;edge>0;edge--,mask>>=1) {
      /* set rsh of hc, fire, and collect lhs responses */
      (id<mask) ? PCTFS_rvec_zero(lhs,m) : PCTFS_rvec_set(lhs,1.0,m);
      PCTFS_gs_gop_hc(PCTFS_gs_handle,lhs,"+\0",edge);

      /* set lsh of hc, fire, and collect rhs responses */
      (id<mask) ? PCTFS_rvec_set(rhs,1.0,m) : PCTFS_rvec_zero(rhs,m);
      PCTFS_gs_gop_hc(PCTFS_gs_handle,rhs,"+\0",edge);

      /* count number of dofs I own that have signal and not in sep set */
      for (PCTFS_ivec_zero(sum,4),ct=i=0;i<n;i++) {
        if (!used[i]) {
          /* number of unmarked dofs on node */
          ct++;
          /* number of dofs to be marked on lhs hc */
          if ((id< mask)&&(lhs[i]!=0.0)) { sum[0]++; }
          /* number of dofs to be marked on rhs hc */
          if ((id>=mask)&&(rhs[i]!=0.0)) { sum[1]++; }
        }
      }

      /* go for load balance - choose half with most unmarked dofs, bias LHS */
      (id<mask) ? (sum[2]=ct) : (sum[3]=ct);
      PCTFS_giop_hc(sum,w,4,op,edge);

      /* lhs hc wins */
      if (sum[2]>=sum[3]) {
        if (id<mask) {
          /* mark dofs I own that have signal and not in sep set */
          for (ct=i=0;i<n;i++) {
            if ((!used[i])&&(lhs[i]!=0.0)) {
              ct++; nfo++;
              *--iptr = local2global[i];
              used[i]=edge;
            }
          }
          if (ct>1) { PCTFS_ivec_sort(iptr,ct); }
          lnsep[edge]=ct;
        }
        nsep[edge]=sum[0];
        dir [edge]=LEFT;
      } else { /* rhs hc wins */
        if (id>=mask) {
          /* mark dofs I own that have signal and not in sep set */
          for (ct=i=0;i<n;i++) {
            if ((!used[i])&&(rhs[i]!=0.0)) {
              ct++; nfo++;
              *--iptr = local2global[i];
              used[i]=edge;
            }
          }
          if (ct>1) {PCTFS_ivec_sort(iptr,ct);}
          lnsep[edge]=ct;
        }
        nsep[edge]=sum[1];
        dir [edge]=RIGHT;
      }
      /* LATER or we can recur on these to order seps at this level */
      /* do we need full set of separators for this?                */

      /* fold rhs hc into lower */
      if (id>=mask) { id-=mask; }
    }
  }


  /* level 0 is on processor case - so mark the remainder */
  for (ct=i=0;i<n;i++) {
    if (!used[i]) {
      ct++; nfo++;
      *--iptr = local2global[i];
      used[i]=edge;
    }
  }
  if (ct>1) { PCTFS_ivec_sort(iptr,ct); }
  lnsep[edge]=ct;
  nsep [edge]=ct;
  dir  [edge]=LEFT;

  xxt_handle->info->nsep=nsep;
  xxt_handle->info->lnsep=lnsep;
  xxt_handle->info->fo=fo;
  xxt_handle->info->nfo=nfo;

  free(dir);
  free(lhs);
  free(rhs);
  free(used);
  PetscFunctionReturn(0);
}

/**************************************xxt.c***********************************/
static mv_info *set_mvi(PetscInt *local2global, PetscInt n, PetscInt m, void *matvec, void *grid_data)
{
  mv_info *mvi;


  mvi = (mv_info*)malloc(sizeof(mv_info));
  mvi->n=n;
  mvi->m=m;
  mvi->n_global=-1;
  mvi->m_global=-1;
  mvi->local2global=(PetscInt*)malloc((m+1)*sizeof(PetscInt));
  PCTFS_ivec_copy(mvi->local2global,local2global,m);
  mvi->local2global[m] = INT_MAX;
  mvi->matvec=(PetscErrorCode (*)(mv_info*,PetscScalar*,PetscScalar*))matvec;
  mvi->grid_data=grid_data;

  /* set xxt communication handle to perform restricted matvec */
  mvi->PCTFS_gs_handle = PCTFS_gs_init(local2global, m, PCTFS_num_nodes);

  return(mvi);
}

/**************************************xxt.c***********************************/
static PetscErrorCode do_matvec(mv_info *A, PetscScalar *v, PetscScalar *u)
{
  PetscFunctionBegin;
  A->matvec((mv_info*)A->grid_data,v,u);
  PetscFunctionReturn(0);
}