On 8/1/17 2:16 PM, Barry Smith wrote:
On Aug 1, 2017, at 3:29 AM, Lisandro Dalcin <[email protected]> wrote:
On 31 July 2017 at 19:50, Barry Smith <[email protected]> wrote:
Or maybe we just need to rethink our default max_steps and max_time.
What about the following:
* TSCreate()
max_steps = PETSC_MAX_INT
max_time = PETSC_MAX_REAL (or maybe PETSC_INFINITY? )
* TSSolve()/TSStep()
Error if both max_step and max time are set to unlimited.
I would only error if max_time is infinite. I think it is reasonable to say, "solve this
problem to time T and I don't care how many time steps it takes". While it is not reasonable
to say "integrate this equation forever".
But IMHO it is also reasonable to use -ts_adapt_type none
-ts_max_steps <n> -ts_dt <dt>, without specifying a maximum time. If
you don't set the final time, the previous example will fail despite
the solver not integrating forever but stopping after <n> steps. My
proposal gives users maximum freedom about how to terminate the
integration. Is there anything wrong with my reasoning?
No you're reasoning is ok. But I don't really understand why one would do
-ts_adapt_type none -ts_max_steps <n> -ts_dt <dt>
That is just an obscure way of setting a final time; better to have the user
set the final time. It is clearer to both them and the code what they are
doing. If they forget to set adapt none then they could end up with any strange
final time they had no control over.
Well, there are situations in which you want to do a certain number of
fixed steps. Moreover, there are methods that do not have adaptors so
setting the exact final time will not work. I guess one can set a final
time that exceeds n*dt by some margin. In the end I don't think it
really matters because none would be intuitive for all use cases. I
think it would be useful to document it really well (with use-case
examples). I don't know how to do that so the users find it easy and
easy to understand.
Emil
Barry
--
Lisandro Dalcin
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