Get read-only pointer to contiguous array containing this processor’s portion of the vector data.
x - the vector
a - the array
The array must be returned using a matching call to VecRestoreArrayRead().
Unlike VecGetArray(), this routine is not collective and preserves cached information like vector norms.
Standard PETSc vectors use contiguous storage so that this routine does not perform a copy. Other vector implementations may require a copy, but must such implementations should cache the contiguous representation so that only one copy is performed when this routine is called multiple times in sequence.