2: static char help[] = "Tests reusing MPI parallel matrices and MatGetValues().\n\
  3: To test the parallel matrix assembly, this example intentionally lays out\n\
  4: the matrix across processors differently from the way it is assembled.\n\
  5: This example uses bilinear elements on the unit square.  Input arguments are:\n\
  6:   -m <size> : problem size\n\n";

  8:  #include <petscmat.h>

 10: int FormElementStiffness(PetscReal H,PetscScalar *Ke)
 11: {
 13:   Ke[0]  = H/6.0;    Ke[1]  = -.125*H; Ke[2]  = H/12.0;   Ke[3]  = -.125*H;
 14:   Ke[4]  = -.125*H;  Ke[5]  = H/6.0;   Ke[6]  = -.125*H;  Ke[7]  = H/12.0;
 15:   Ke[8]  = H/12.0;   Ke[9]  = -.125*H; Ke[10] = H/6.0;    Ke[11] = -.125*H;
 16:   Ke[12] = -.125*H;  Ke[13] = H/12.0;  Ke[14] = -.125*H;  Ke[15] = H/6.0;
 17:   return(0);
 18: }

 20: int main(int argc,char **args)
 21: {
 22:   Mat            C;
 23:   Vec            u,b;
 25:   PetscMPIInt    size,rank;
 26:   PetscInt       i,m = 5,N,start,end,M,idx[4];
 27:   PetscInt       j,nrsub,ncsub,*rsub,*csub,mystart,myend;
 28:   PetscBool      flg;
 29:   PetscScalar    one = 1.0,Ke[16],*vals;
 30:   PetscReal      h,norm;

 32:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 33:   PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL);

 35:   N    = (m+1)*(m+1); /* dimension of matrix */
 36:   M    = m*m;      /* number of elements */
 37:   h    = 1.0/m;    /* mesh width */
 38:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 39:   MPI_Comm_size(PETSC_COMM_WORLD,&size);

 41:   /* Create stiffness matrix */
 42:   MatCreate(PETSC_COMM_WORLD,&C);
 43:   MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,N,N);
 44:   MatSetFromOptions(C);
 45:   MatSetUp(C);

 47:   start = rank*(M/size) + ((M%size) < rank ? (M%size) : rank);
 48:   end   = start + M/size + ((M%size) > rank);

 50:   /* Form the element stiffness for the Laplacian */
 51:   FormElementStiffness(h*h,Ke);
 52:   for (i=start; i<end; i++) {
 53:     /* location of lower left corner of element */
 54:     /* node numbers for the four corners of element */
 55:     idx[0] = (m+1)*(i/m) + (i % m);
 56:     idx[1] = idx[0]+1; idx[2] = idx[1] + m + 1; idx[3] = idx[2] - 1;
 57:     MatSetValues(C,4,idx,4,idx,Ke,ADD_VALUES);
 58:   }
 59:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
 60:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);

 62:   /* Assemble the matrix again */
 63:   MatZeroEntries(C);

 65:   for (i=start; i<end; i++) {
 66:     /* location of lower left corner of element */
 67:     /* node numbers for the four corners of element */
 68:     idx[0] = (m+1)*(i/m) + (i % m);
 69:     idx[1] = idx[0]+1; idx[2] = idx[1] + m + 1; idx[3] = idx[2] - 1;
 70:     MatSetValues(C,4,idx,4,idx,Ke,ADD_VALUES);
 71:   }
 72:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
 73:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);

 75:   /* Create test vectors */
 76:   VecCreate(PETSC_COMM_WORLD,&u);
 77:   VecSetSizes(u,PETSC_DECIDE,N);
 78:   VecSetFromOptions(u);
 79:   VecDuplicate(u,&b);
 80:   VecSet(u,one);

 82:   /* Check error */
 83:   MatMult(C,u,b);
 84:   VecNorm(b,NORM_2,&norm);
 85:   if (norm > PETSC_SQRT_MACHINE_EPSILON) {
 86:     PetscPrintf(PETSC_COMM_WORLD,"Norm of error b %g should be near 0\n",(double)norm);
 87:   }

 89:   /* Now test MatGetValues() */
 90:   PetscOptionsHasName(NULL,NULL,"-get_values",&flg);
 91:   if (flg) {
 92:     MatGetOwnershipRange(C,&mystart,&myend);
 93:     nrsub = myend - mystart; ncsub = 4;
 94:     PetscMalloc1(nrsub*ncsub,&vals);
 95:     PetscMalloc1(nrsub,&rsub);
 96:     PetscMalloc1(ncsub,&csub);
 97:     for (i=myend-1; i>=mystart; i--) rsub[myend-i-1] = i;
 98:     for (i=0; i<ncsub; i++) csub[i] = 2*(ncsub-i) + mystart;
 99:     MatGetValues(C,nrsub,rsub,ncsub,csub,vals);
100:     MatView(C,PETSC_VIEWER_STDOUT_WORLD);
101:     PetscSynchronizedPrintf(PETSC_COMM_WORLD,"processor number %d: start=%D, end=%D, mystart=%D, myend=%D\n",rank,start,end,mystart,myend);
102:     for (i=0; i<nrsub; i++) {
103:       for (j=0; j<ncsub; j++) {
104:         if (PetscImaginaryPart(vals[i*ncsub+j]) != 0.0) {
105:           PetscSynchronizedPrintf(PETSC_COMM_WORLD,"  C[%D, %D] = %g + %g i\n",rsub[i],csub[j],(double)PetscRealPart(vals[i*ncsub+j]),(double)PetscImaginaryPart(vals[i*ncsub+j]));
106:         } else {
107:           PetscSynchronizedPrintf(PETSC_COMM_WORLD,"  C[%D, %D] = %g\n",rsub[i],csub[j],(double)PetscRealPart(vals[i*ncsub+j]));
108:         }
109:       }
110:     }
111:     PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);
112:     PetscFree(rsub);
113:     PetscFree(csub);
114:     PetscFree(vals);
115:   }

117:   /* Free data structures */
118:   VecDestroy(&u);
119:   VecDestroy(&b);
120:   MatDestroy(&C);
121:   PetscFinalize();
122:   return ierr;
123: }




128: /*TEST

130:    test:
131:       nsize: 4

133: TEST*/