[petsc-dev] TS Terminology

[Matthew Knepley]

On Fri, Oct 20, 2017 at 9:23 AM, Emil Constantinescu <emconsta at mcs.anl.gov>
wrote:

> 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.
>

This is not "internal". Its the toplevel interface:


https://bitbucket.org/petsc/petsc/src/63ae3ecac3af8ce782273a76ad4152cddc2fd80a/src/ts/interface/ts.c?at=master&fileviewer=file-view-default#ts.c-884

It computes F - G.

   Matt


> 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/>
>>
>


-- 
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/>
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