[petsc-dev] TS Terminology

[Emil Constantinescu]

On 10/20/17 7:57 AM, Matthew Knepley wrote:
> I am confused by some of the terminology in TS. At the top level, 
> IFunction appears to mean the entire equation
> 
>    F(u, u_t, x) = 0

Matt, page 141 of the manual: F(t, u, u_t) = G(t, u), and not zero on 
the RHS side. To make the interface general we allow internally for F:= 
F(t, u, u_t) - G(t, u) and then F=0.

Emil

PS: Manual: PETSc 3.8 September 26, 2017

> However, this appears to mean something different than ifunction at the 
> function pointer level. Inside TSCompiteIFunction(), it uses both 
> ifunction and rhsfunction. This makes it hard to understand how 
> composition works. TSComputeRHS() is called inside TSComputeIFunction(), 
> so if we want to reuse vectors it should not initialize the vector, but 
> it seems like TSComputeIFunction() should initialize the vector since 
> TSComputeIFunctionLocal() does.
> 
> What guarantees about initialization should we have?
> 
>     Matt
> 
> -- 
> What most experimenters take for granted before they begin their 
> experiments is infinitely more interesting than any results to which 
> their experiments lead.
> -- Norbert Wiener
> 
> https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>