Actual source code: ex27.c

petsc-3.7.1 2016-05-15
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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);

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

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

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

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

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

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

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

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

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

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

110:   /* Sove preconditioned system A*x = b */
111:   KSPSolve(ksp,b,x);
112:   KSPGetIterationNumber(ksp,&its);

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

121:   /* Free work space.  */
122:   MatDestroy(&X);
123:   MatDestroy(&A); VecDestroy(&b);
124:   VecDestroy(&u); VecDestroy(&x);
125:   KSPDestroy(&ksp);
126:   PetscFinalize();
127:   return 0;
128: }

132: PetscErrorCode PCShellApply_Matinv(PC pc,Vec xin,Vec xout)
133: {
135:   Mat            X;

138:   PCShellGetContext(pc,(void**)&X);
139:   MatMult(X,xin,xout);
140:   return(0);
141: }