Example with multiple RHS?

[johnomotani]

Similar issue to #1223, and might be addressed by a solution to that, but a bit more generic: it would be nice if there was an example that shows how to re-use a preconditioner for multiple RHS vectors, as often happens in a time-evolution (initial value) code. My first interest is the case when the matrix does not change, but if there is any possibility to update the matrix more efficiently than starting from scratch (e.g. when the pattern of non-zeros does not change?) that would be great to have in addition.