[petsc-users] TS question 1: how to stop explicit methods because they do not use SNES(VI)?

[Emil Constantinescu]

On 2/14/17 6:53 AM, Matthew Knepley wrote:
>
>     Explicit methods use only RHSFunction and ignore IFunction, so in
>     your case, if you change TS type to rk and ssp at run time, you are
>     actually solving u_t = G(t,u). If RHSFunction is not provided, PETSc
>     will assume the RHS is zero (u_t=0).
>
>
> I do not agree with this. I thought our aim was to support users
> comparing explicit with implicit with semi-implicit. This breaks that
> model completely.

Matt, all RHSFunction can be turned into IFunction but not the other way 
around. Explicit TS solvers cannot deal with all forms of IFunction and 
providing support for classifying them may be burdensome and difficult 
to scale. I think it's more lucrative to improve the documentation.

Emil