#include <petscksp.h>

int main(int argc,char **args)
{
  Vec            u,b;
  Mat            A;
  KSP            ksp;
  PetscViewer    viewer;
  PetscInt       n_rows, n_cols;
  PetscErrorCode ierr;

  char filename[] = "./test.mat";

  PetscInitialize(&argc,&args,(char*)0,"");

  ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD,filename,FILE_MODE_READ,&viewer);CHKERRQ(ierr);

  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetFromOptions(A);CHKERRQ(ierr);
  ierr = MatLoad(A,viewer);CHKERRQ(ierr);

  ierr = PetscViewerDestroy(&viewer);CHKERRQ(ierr);

  ierr = MatGetSize(A,&n_rows,&n_cols);CHKERRQ(ierr);

  ierr = VecCreate(PETSC_COMM_WORLD,&b);CHKERRQ(ierr);
  ierr = VecSetSizes(b,n_rows,PETSC_DECIDE);CHKERRQ(ierr);
  ierr = VecSetFromOptions(b);CHKERRQ(ierr);

  ierr = VecDuplicate(b,&u);CHKERRQ(ierr);

  ierr = VecSet(b,1.0);CHKERRQ(ierr);

  ierr = KSPCreate(PETSC_COMM_WORLD,&ksp);CHKERRQ(ierr);
  ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr);
  ierr = KSPSetOperators(ksp,A,A);CHKERRQ(ierr);
  ierr = KSPSolve(ksp,b,u);CHKERRQ(ierr);

  ierr = KSPDestroy(&ksp);CHKERRQ(ierr);
  ierr = MatDestroy(&A);CHKERRQ(ierr);

  ierr = PetscFinalize();

  return 0;
}