KSPSetOperators

[Yixun Liu]

Hi,
In ksp/ex2.c

/*
     Set operators. Here the matrix that defines the linear system
     also serves as the preconditioning matrix.
  */
  ierr = KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);CHKERRQ(ierr);

The matrix related with linear system is same with the preconditioning
matrix, why set the flat to be DIFFERENT_NONZERO_PATTERN?

Thanks.