Actual source code: ex16.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Reads a matrix from PETSc binary file. Use for view or investigating matrix data structure. \n\n";
      3: /*
      4:  Example:
      5:       ./ex16 -f <matrix file> -a_mat_view draw -draw_pause -1
      6:       ./ex16 -f <matrix file> -a_mat_view ::ascii_info
      7:  */

      9: #include <petscmat.h>
     12: int main(int argc,char **args)
     13: {
     14:   Mat               A,Asp;
     15:   PetscViewer       fd;                        /* viewer */
     16:   char              file[PETSC_MAX_PATH_LEN];  /* input file name */
     17:   PetscErrorCode    ierr;
     18:   PetscInt          m,n,rstart,rend;
     19:   PetscBool         flg;
     20:   PetscInt          row,ncols,j,nrows,nnzA=0,nnzAsp=0;
     21:   const PetscInt    *cols;
     22:   const PetscScalar *vals;
     23:   PetscReal         norm,percent,val,dtol=1.e-16;
     24:   PetscMPIInt       rank;
     25:   MatInfo           matinfo;
     26:   PetscInt          Dnnz,Onnz;

     29:   PetscInitialize(&argc,&args,(char*)0,help);
     30:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     32:   /* Determine files from which we read the linear systems. */
     33:   PetscOptionsGetString(NULL,"-f",file,PETSC_MAX_PATH_LEN,&flg);
     34:   if (!flg) SETERRQ(PETSC_COMM_WORLD,1,"Must indicate binary file with the -f option");

     36:   /* Open binary file.  Note that we use FILE_MODE_READ to indicate
     37:      reading from this file. */
     38:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,file,FILE_MODE_READ,&fd);

     40:   /* Load the matrix; then destroy the viewer. */
     41:   MatCreate(PETSC_COMM_WORLD,&A);
     42:   MatSetOptionsPrefix(A,"a_");
     43:   MatSetFromOptions(A);
     44:   MatLoad(A,fd);
     45:   PetscViewerDestroy(&fd);
     46:   MatGetSize(A,&m,&n);
     47:   MatGetInfo(A,MAT_LOCAL,&matinfo);
     48:   /*printf("matinfo.nz_used %g\n",matinfo.nz_used);*/

     50:   /* Get a sparse matrix Asp by dumping zero entries of A */
     51:   MatCreate(PETSC_COMM_WORLD,&Asp);
     52:   MatSetSizes(Asp,m,n,PETSC_DECIDE,PETSC_DECIDE);
     53:   MatSetOptionsPrefix(Asp,"asp_");
     54:   MatSetFromOptions(Asp);
     55:   Dnnz = (PetscInt)matinfo.nz_used/m + 1;
     56:   Onnz = Dnnz/2;
     57:   printf("Dnnz %d %d\n",Dnnz,Onnz);
     58:   MatSeqAIJSetPreallocation(Asp,Dnnz,NULL);
     59:   MatMPIAIJSetPreallocation(Asp,Dnnz,NULL,Onnz,NULL);
     60:   /* The allocation above is approximate so we must set this option to be permissive.
     61:    * Real code should preallocate exactly. */
     62:   MatSetOption(Asp,MAT_NEW_NONZERO_LOCATION_ERR,PETSC_FALSE);

     64:   /* Check zero rows */
     65:   MatGetOwnershipRange(A,&rstart,&rend);
     66:   nrows = 0;
     67:   for (row=rstart; row<rend; row++) {
     68:     MatGetRow(A,row,&ncols,&cols,&vals);
     69:     nnzA += ncols;
     70:     norm  = 0.0;
     71:     for (j=0; j<ncols; j++) {
     72:       val = PetscAbsScalar(vals[j]);
     73:       if (norm < val) norm = norm;
     74:       if (val > dtol) {
     75:         MatSetValues(Asp,1,&row,1,&cols[j],&vals[j],INSERT_VALUES);
     76:         nnzAsp++;
     77:       }
     78:     }
     79:     if (!norm) nrows++;
     80:     MatRestoreRow(A,row,&ncols,&cols,&vals);
     81:   }
     82:   MatAssemblyBegin(Asp,MAT_FINAL_ASSEMBLY);
     83:   MatAssemblyEnd(Asp,MAT_FINAL_ASSEMBLY);

     85:   percent=(PetscReal)nnzA*100/(m*n);
     86:   PetscPrintf(PETSC_COMM_SELF," [%d] Matrix A local size %d,%d; nnzA %d, %g percent; No. of zero rows: %d\n",rank,m,n,nnzA,percent,nrows);
     87:   percent=(PetscReal)nnzAsp*100/(m*n);
     88:   PetscPrintf(PETSC_COMM_SELF," [%d] Matrix Asp nnzAsp %d, %g percent\n",rank,nnzAsp,percent);

     90:   /* investigate matcoloring for Asp */
     91:   PetscBool Asp_coloring = PETSC_FALSE;
     92:   PetscOptionsHasName(NULL,"-Asp_color",&Asp_coloring);
     93:   if (Asp_coloring) {
     94:     ISColoring    iscoloring;
     95:     MatFDColoring matfdcoloring;
     96:     PetscPrintf(PETSC_COMM_WORLD," Create coloring of Asp...\n");
     97:     MatGetColoring(Asp,MATCOLORINGSL,&iscoloring);
     98:     MatFDColoringCreate(Asp,iscoloring,&matfdcoloring);
     99:     MatFDColoringSetFromOptions(matfdcoloring);
    100:     /*MatFDColoringView(matfdcoloring,PETSC_VIEWER_STDOUT_WORLD);*/
    101:     ISColoringDestroy(&iscoloring);
    102:     MatFDColoringDestroy(&matfdcoloring);
    103:   }

    105:   /* Write Asp in binary for study - see ~petsc/src/mat/examples/tests/ex124.c */
    106:   PetscBool Asp_write = PETSC_FALSE;
    107:   PetscOptionsHasName(NULL,"-Asp_write",&Asp_write);
    108:   if (Asp_write) {
    109:     PetscViewer viewer;
    110:     PetscPrintf(PETSC_COMM_SELF,"Write Asp into file Asp.dat ...\n");
    111:     PetscViewerBinaryOpen(PETSC_COMM_WORLD,"Asp.dat",FILE_MODE_WRITE,&viewer);
    112:     MatView(Asp,viewer);
    113:     PetscViewerDestroy(&viewer);
    114:   }

    116:   MatDestroy(&A);
    117:   MatDestroy(&Asp);
    118:   PetscFinalize();
    119:   return 0;
    120: }