Actual source code: ex18.c

petsc-3.4.2 2013-07-02
  2: static char help[] = "Reads a PETSc matrix and vector from a file and solves a linear system.\n\
  3: Input arguments are:\n\
  4:   -f <input_file> : file to load.  For example see $PETSC_DIR/share/petsc/datafiles/matrices\n\n";

  6: #include <petscmat.h>
  7: #include <petscksp.h>
  8: #include <petsctime.h>

 12: int main(int argc,char **args)
 13: {
 15:   PetscInt       its,m,n,mvec;
 16:   PetscLogDouble time1,time2,time;
 17:   PetscReal      norm;
 18:   Vec            x,b,u;
 19:   Mat            A;
 20:   KSP            ksp;
 21:   char           file[PETSC_MAX_PATH_LEN];
 22:   PetscViewer    fd;
 23:   PetscLogStage  stage1;

 25:   PetscInitialize(&argc,&args,(char*)0,help);

 27:   /* Read matrix and RHS */
 28:   PetscOptionsGetString(NULL,"-f",file,PETSC_MAX_PATH_LEN,NULL);
 29:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,file,FILE_MODE_READ,&fd);
 30:   MatCreate(PETSC_COMM_WORLD,&A);
 31:   MatSetType(A,MATSEQAIJ);
 32:   MatLoad(A,fd);
 33:   VecCreate(PETSC_COMM_WORLD,&b);
 34:   VecLoad(b,fd);
 35:   PetscViewerDestroy(&fd);

 37:   /*
 38:      If the load matrix is larger then the vector, due to being padded
 39:      to match the blocksize then create a new padded vector
 40:   */
 41:   MatGetSize(A,&m,&n);
 42:   VecGetSize(b,&mvec);
 43:   if (m > mvec) {
 44:     Vec         tmp;
 45:     PetscScalar *bold,*bnew;
 46:     /* create a new vector b by padding the old one */
 47:     VecCreate(PETSC_COMM_WORLD,&tmp);
 48:     VecSetSizes(tmp,PETSC_DECIDE,m);
 49:     VecSetFromOptions(tmp);
 50:     VecGetArray(tmp,&bnew);
 51:     VecGetArray(b,&bold);
 52:     PetscMemcpy(bnew,bold,mvec*sizeof(PetscScalar));
 53:     VecDestroy(&b);
 54:     b    = tmp;
 55:   }

 57:   /* Set up solution */
 58:   VecDuplicate(b,&x);
 59:   VecDuplicate(b,&u);
 60:   VecSet(x,0.0);

 62:   /* Solve system */
 63:   PetscLogStageRegister("Stage 1",&stage1);
 64:   PetscLogStagePush(stage1);
 65:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 66:   KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);
 67:   KSPSetFromOptions(ksp);
 68:   PetscTime(&time1);
 69:   KSPSolve(ksp,b,x);
 70:   PetscTime(&time2);
 71:   time = time2 - time1;
 72:   PetscLogStagePop();

 74:   /* Show result */
 75:   MatMult(A,x,u);
 76:   VecAXPY(u,-1.0,b);
 77:   VecNorm(u,NORM_2,&norm);
 78:   KSPGetIterationNumber(ksp,&its);
 79:   PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
 80:   PetscPrintf(PETSC_COMM_WORLD,"Residual norm %G\n",norm);
 81:   PetscPrintf(PETSC_COMM_WORLD,"Time for solve = %5.2f seconds\n",time);

 83:   /* Cleanup */
 84:   KSPDestroy(&ksp);
 85:   VecDestroy(&x);
 86:   VecDestroy(&b);
 87:   VecDestroy(&u);
 88:   MatDestroy(&A);

 90:   PetscFinalize();
 91:   return 0;
 92: }