Actual source code: ex21.c

petsc-3.7.3 2016-07-24
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  1: static const char help[] = "Tests MatGetSchurComplement\n";

  3: #include <petscksp.h>


  8: PetscErrorCode Create(MPI_Comm comm,Mat *inA,IS *is0,IS *is1)
  9: {
 11:   Mat            A;
 12:   PetscInt       r,rend,M;
 13:   PetscMPIInt    rank;

 16:   *inA = 0;
 17:   MatCreate(comm,&A);
 18:   MatSetSizes(A,4,4,PETSC_DETERMINE,PETSC_DETERMINE);
 19:   MatSetFromOptions(A);
 20:   MatSetUp(A);
 21:   MatGetOwnershipRange(A,&r,&rend);
 22:   MatGetSize(A,&M,NULL);

 24:   ISCreateStride(comm,2,r,1,is0);
 25:   ISCreateStride(comm,2,r+2,1,is1);

 27:   MPI_Comm_rank(comm,&rank);

 29:   {
 30:     PetscInt    rows[4],cols0[5],cols1[5],cols2[3],cols3[3];
 31:     PetscScalar RR = 1000.*rank,vals0[5],vals1[4],vals2[3],vals3[3];

 33:     rows[0]            = r;
 34:     rows[1]            = r+1;
 35:     rows[2]            = r+2;
 36:     rows[3]            = r+3;

 38:     cols0[0]           = r+0;
 39:     cols0[1]           = r+1;
 40:     cols0[2]           = r+3;
 41:     cols0[3]           = (r+4)%M;
 42:     cols0[4]           = (r+M-4)%M;

 44:     cols1[0]           = r+1;
 45:     cols1[1]           = r+2;
 46:     cols1[2]           = (r+4+1)%M;
 47:     cols1[3]           = (r+M-4+1)%M;

 49:     cols2[0]           = r;
 50:     cols2[1]           = r+2;
 51:     cols2[2]           = (r+4+2)%M;

 53:     cols3[0]           = r+1;
 54:     cols3[1]           = r+3;
 55:     cols3[2]           = (r+4+3)%M;

 57:     vals0[0] = RR+1.;
 58:     vals0[1] = RR+2.;
 59:     vals0[2] = RR+3.;
 60:     vals0[3] = RR+4.;
 61:     vals0[4] = RR+5.;

 63:     vals1[0] = RR+6.;
 64:     vals1[1] = RR+7.;
 65:     vals1[2] = RR+8.;
 66:     vals1[3] = RR+9.;

 68:     vals2[0] = RR+10.;
 69:     vals2[1] = RR+11.;
 70:     vals2[2] = RR+12.;

 72:     vals3[0] = RR+13.;
 73:     vals3[1] = RR+14.;
 74:     vals3[2] = RR+15.;
 75:     MatSetValues(A,1,&rows[0],5,cols0,vals0,INSERT_VALUES);
 76:     MatSetValues(A,1,&rows[1],4,cols1,vals1,INSERT_VALUES);
 77:     MatSetValues(A,1,&rows[2],3,cols2,vals2,INSERT_VALUES);
 78:     MatSetValues(A,1,&rows[3],3,cols3,vals3,INSERT_VALUES);
 79:   }
 80:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 81:   MatAssemblyEnd  (A,MAT_FINAL_ASSEMBLY);
 82:   *inA = A;
 83:   return(0);
 84: }

 88: PetscErrorCode Destroy(Mat *A,IS *is0,IS *is1)
 89: {

 93:   MatDestroy(A);
 94:   ISDestroy(is0);
 95:   ISDestroy(is1);
 96:   return(0);
 97: }

101: int main(int argc,char *argv[])
102: {
104:   Mat            A,S = NULL,Sexplicit = NULL;
105:   IS             is0,is1;

107:   PetscInitialize(&argc,&argv,0,help);

110:   /* Test the Schur complement one way */
111:   Create(PETSC_COMM_WORLD,&A,&is0,&is1);
112:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);
113:   ISView(is0,PETSC_VIEWER_STDOUT_WORLD);
114:   ISView(is1,PETSC_VIEWER_STDOUT_WORLD);
115:   MatGetSchurComplement(A,is0,is0,is1,is1,MAT_INITIAL_MATRIX,&S,MAT_SCHUR_COMPLEMENT_AINV_DIAG,MAT_IGNORE_MATRIX,NULL);
116:   MatComputeExplicitOperator(S,&Sexplicit);
117:   PetscPrintf(PETSC_COMM_WORLD,"\nExplicit Schur complement of (0,0) in (1,1)\n");
118:   MatView(Sexplicit,PETSC_VIEWER_STDOUT_WORLD);
119:   Destroy(&A,&is0,&is1);
120:   MatDestroy(&S);
121:   MatDestroy(&Sexplicit);

123:   /* And the other */
124:   Create(PETSC_COMM_WORLD,&A,&is0,&is1);
125:   MatGetSchurComplement(A,is1,is1,is0,is0,MAT_INITIAL_MATRIX,&S,MAT_SCHUR_COMPLEMENT_AINV_DIAG,MAT_IGNORE_MATRIX,NULL);
126:   MatComputeExplicitOperator(S,&Sexplicit);
127:   PetscPrintf(PETSC_COMM_WORLD,"\nExplicit Schur complement of (1,1) in (0,0)\n");
128:   MatView(Sexplicit,PETSC_VIEWER_STDOUT_WORLD);
129:   Destroy(&A,&is0,&is1);
130:   MatDestroy(&S);
131:   MatDestroy(&Sexplicit);

133:   /* This time just the preconditioning matrix. */
134:   Create(PETSC_COMM_WORLD,&A,&is0,&is1);
135:   MatGetSchurComplement(A,is0,is0,is1,is1,MAT_IGNORE_MATRIX,NULL,MAT_SCHUR_COMPLEMENT_AINV_DIAG,MAT_INITIAL_MATRIX,&S);
136:   PetscPrintf(PETSC_COMM_WORLD,"\nPreconditioning Schur complement of (0,0) in (1,1)\n");
137:   MatView(S,PETSC_VIEWER_STDOUT_WORLD);
138:   /* Modify and refresh */
139:   MatShift(A,1.);
140:   MatGetSchurComplement(A,is0,is0,is1,is1,MAT_IGNORE_MATRIX,NULL,MAT_SCHUR_COMPLEMENT_AINV_DIAG,MAT_REUSE_MATRIX,&S);
141:   PetscPrintf(PETSC_COMM_WORLD,"\nAfter update\n");
142:   MatView(S,PETSC_VIEWER_STDOUT_WORLD);
143:   Destroy(&A,&is0,&is1);
144:   MatDestroy(&S);

146:   PetscFinalize();
147:   return 0;
148: }