On 10/20/17 9:11 AM, Matthew Knepley wrote:
On Fri, Oct 20, 2017 at 9:23 AM, Emil Constantinescu
<[email protected] <mailto:[email protected]>> 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.
That's what it should do in some cases. The user provides either
ifunction or rhs funtion or both. The api to the solvers can take care
of this stuff automatically - that's what I meant by internal. Different
TS solvers can take different definitions of the funtions; e.g., imex
need both, beuler can take ifuntion and/or rhs function but instead of
writing beuler for both we choose the most general case (ifunction) and
compose the functions accordingly. The F - G is transparent to the user.
But somewhere the sausage needs to be made and I think that is the right
level because that is least likely to change and least maintenance.
Emil
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/
<https://www.cse.buffalo.edu/~knepley/>
<http://www.caam.rice.edu/~mk51/ <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/>
