Actual source code: ex27.c

petsc-3.12.1 2019-10-22
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  2: static char help[] = "Reads a PETSc matrix and vector from a file and solves a linear system.\n\
  3: Test MatMatSolve().  Input parameters include\n\
  4:   -f <input_file> : file to load \n\n";

  6: /*
  7:   Usage:
  8:      ex27 -f0 <mat_binaryfile>
  9: */

 11:  #include <petscksp.h>
 12: extern PetscErrorCode PCShellApply_Matinv(PC,Vec,Vec);

 14: int main(int argc,char **args)
 15: {
 16:   KSP            ksp;
 17:   Mat            A,B,F,X;
 18:   Vec            x,b,u;          /* approx solution, RHS, exact solution */
 19:   PetscViewer    fd;             /* viewer */
 20:   char           file[1][PETSC_MAX_PATH_LEN];     /* input file name */
 21:   PetscBool      flg;
 23:   PetscInt       M,N,i,its;
 24:   PetscReal      norm;
 25:   PetscScalar    val=1.0;
 26:   PetscMPIInt    size;
 27:   PC             pc;

 29:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 30:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 31:   if (size != 1) SETERRQ(PETSC_COMM_WORLD,PETSC_ERR_SUP,"This is a uniprocessor example only!");

 33:   /* Read matrix and right-hand-side vector */
 34:   PetscOptionsGetString(NULL,NULL,"-f",file[0],PETSC_MAX_PATH_LEN,&flg);
 35:   if (!flg) SETERRQ(PETSC_COMM_WORLD,PETSC_ERR_USER,"Must indicate binary file with the -f option");

 37:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,file[0],FILE_MODE_READ,&fd);
 38:   MatCreate(PETSC_COMM_WORLD,&A);
 39:   MatSetType(A,MATAIJ);
 40:   MatLoad(A,fd);
 41:   VecCreate(PETSC_COMM_WORLD,&b);
 42:   VecLoad(b,fd);
 43:   PetscViewerDestroy(&fd);

 45:   /*
 46:      If the loaded matrix is larger than the vector (due to being padded
 47:      to match the block size of the system), then create a new padded vector.
 48:   */
 49:   {
 50:     PetscInt    m,n,j,mvec,start,end,indx;
 51:     Vec         tmp;
 52:     PetscScalar *bold;

 54:     /* Create a new vector b by padding the old one */
 55:     MatGetLocalSize(A,&m,&n);
 56:     if (m != n) SETERRQ2(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ, "This example is not intended for rectangular matrices (%D, %D)", m, n);
 57:     VecCreate(PETSC_COMM_WORLD,&tmp);
 58:     VecSetSizes(tmp,m,PETSC_DECIDE);
 59:     VecSetFromOptions(tmp);
 60:     VecGetOwnershipRange(b,&start,&end);
 61:     VecGetLocalSize(b,&mvec);
 62:     VecGetArray(b,&bold);
 63:     for (j=0; j<mvec; j++) {
 64:       indx = start+j;
 65:       VecSetValues(tmp,1,&indx,bold+j,INSERT_VALUES);
 66:     }
 67:     VecRestoreArray(b,&bold);
 68:     VecDestroy(&b);
 69:     VecAssemblyBegin(tmp);
 70:     VecAssemblyEnd(tmp);
 71:     b    = tmp;
 72:   }
 73:   VecDuplicate(b,&x);
 74:   VecDuplicate(b,&u);
 75:   VecSet(x,0.0);

 77:   /* Create dense matric B and X. Set B as an identity matrix */
 78:   MatGetSize(A,&M,&N);
 79:   MatCreate(MPI_COMM_SELF,&B);
 80:   MatSetSizes(B,M,N,M,N);
 81:   MatSetType(B,MATSEQDENSE);
 82:   MatSeqDenseSetPreallocation(B,NULL);
 83:   for (i=0; i<M; i++) {
 84:     MatSetValues(B,1,&i,1,&i,&val,INSERT_VALUES);
 85:   }
 86:   MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
 87:   MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);

 89:   MatDuplicate(B,MAT_DO_NOT_COPY_VALUES,&X);

 91:   /* Compute X=inv(A) by MatMatSolve() */
 92:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 93:   KSPSetOperators(ksp,A,A);
 94:   KSPGetPC(ksp,&pc);
 95:   PCSetType(pc,PCLU);
 96:   KSPSetFromOptions(ksp);
 97:   KSPSetUp(ksp);
 98:   PCFactorGetMatrix(pc,&F);
 99:   MatMatSolve(F,B,X);
100:   MatDestroy(&B);

102:   /* Now, set X=inv(A) as a preconditioner */
103:   PCSetType(pc,PCSHELL);
104:   PCShellSetContext(pc,(void*)X);
105:   PCShellSetApply(pc,PCShellApply_Matinv);
106:   KSPSetFromOptions(ksp);

108:   /* Solve preconditioned system A*x = b */
109:   KSPSolve(ksp,b,x);
110:   KSPGetIterationNumber(ksp,&its);

112:   /* Check error */
113:   MatMult(A,x,u);
114:   VecAXPY(u,-1.0,b);
115:   VecNorm(u,NORM_2,&norm);
116:   PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
117:   PetscPrintf(PETSC_COMM_WORLD,"Residual norm %g\n",(double)norm);

119:   /* Free work space.  */
120:   MatDestroy(&X);
121:   MatDestroy(&A); VecDestroy(&b);
122:   VecDestroy(&u); VecDestroy(&x);
123:   KSPDestroy(&ksp);
124:   PetscFinalize();
125:   return ierr;
126: }

128: PetscErrorCode PCShellApply_Matinv(PC pc,Vec xin,Vec xout)
129: {
131:   Mat            X;

134:   PCShellGetContext(pc,(void**)&X);
135:   MatMult(X,xin,xout);
136:   return(0);
137: }

139: /*TEST

141:     test:
142:       args: -f ${DATAFILESPATH}/matrices/small
143:       requires: datafilespath !complex double !define(PETSC_USE_64BIT_INDICES)
144:       output_file: output/ex27.out

146: TEST*/