[petsc-users] TSSetEventHandler and TSSetPostEventIntervalStep

Tue Oct 27 15:35:11 CDT 2020

Hi Barry,

The code had a different behavior at one point (using the initial timestep after an event) : I still use commit f0e947c45e099a328e78b13737aa9bc4c143ca79 when I really need the time step to get really small after an event. I don't know if it can help with the current code.

Best,

Sophie
________________________________
From: Barry Smith <bsmith at petsc.dev>
Sent: Tuesday, October 27, 2020 16:24
To: Blondel, Sophie <sblondel at utk.edu>
Cc: Matthew Knepley <knepley at gmail.com>; petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>; xolotl-psi-development at lists.sourceforge.net <xolotl-psi-development at lists.sourceforge.net>
Subject: Re: [petsc-users] TSSetEventHandler and TSSetPostEventIntervalStep

  I'm sorry the code is still fundamentally broken, I know I promised a long time ago to fix it all up but it is actually pretty hard to get right.

  It detects the zero by finding a small value when it should detect it by find a small region where it changes sign but surprising it is so hardwired
to the size test that fixing it and testing the new code has been very difficult to me.  My branch is barry/2019-08-18/fix-tsevent-posteventdt

  Barry

On Oct 27, 2020, at 3:02 PM, Blondel, Sophie via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:

Hi Matt,

With the ex40 I attached in my previous email here is what I get printed on screen when running "./ex40 -ts_monitor -ts_event_monitor":
0 TS dt 0.1 time 0.
1 TS dt 0.5 time 0.1
2 TS dt 0.5 time 0.6
3 TS dt 0.5 time 1.1
4 TS dt 0.5 time 1.6
5 TS dt 0.5 time 2.1
6 TS dt 0.5 time 2.6
7 TS dt 0.5 time 3.1
8 TS dt 0.5 time 3.6
9 TS dt 0.5 time 4.1
10 TS dt 0.5 time 4.6
11 TS dt 0.5 time 5.1
12 TS dt 0.5 time 5.6
13 TS dt 0.5 time 6.1
14 TS dt 0.5 time 6.6
15 TS dt 0.5 time 7.1
TSEvent: Event 0 zero crossing at time 7.6 located in 0 iterations
Ball hit the ground at t =  7.60 seconds
16 TS dt 0.5 time 7.6
17 TS dt 0.5 time 8.1
18 TS dt 0.5 time 8.6
19 TS dt 0.5 time 9.1
20 TS dt 0.5 time 9.6
21 TS dt 0.5 time 10.1
22 TS dt 0.5 time 10.6
23 TS dt 0.5 time 11.1
24 TS dt 0.5 time 11.6
25 TS dt 0.5 time 12.1
26 TS dt 0.5 time 12.6
27 TS dt 0.5 time 13.1
28 TS dt 0.5 time 13.6
29 TS dt 0.5 time 14.1
30 TS dt 0.5 time 14.6
31 TS dt 0.5 time 15.1
32 TS dt 0.5 time 15.6
33 TS dt 0.5 time 16.1
34 TS dt 0.5 time 16.6
35 TS dt 0.5 time 17.1
36 TS dt 0.5 time 17.6
37 TS dt 0.5 time 18.1
38 TS dt 0.5 time 18.6
39 TS dt 0.5 time 19.1
40 TS dt 0.5 time 19.6
41 TS dt 0.5 time 20.1
42 TS dt 0.5 time 20.6
43 TS dt 0.5 time 21.1
44 TS dt 0.5 time 21.6
45 TS dt 0.5 time 22.1
46 TS dt 0.5 time 22.6
47 TS dt 0.5 time 23.1
48 TS dt 0.5 time 23.6
49 TS dt 0.5 time 24.1
50 TS dt 0.5 time 24.6
51 TS dt 0.5 time 25.1
TSEvent: Event 0 zero crossing at time 25.6 located in 0 iterations
Ball hit the ground at t = 25.60 seconds
52 TS dt 0.5 time 25.6
53 TS dt 0.5 time 26.1
54 TS dt 0.5 time 26.6
55 TS dt 0.5 time 27.1
56 TS dt 0.5 time 27.6
57 TS dt 0.5 time 28.1
58 TS dt 0.5 time 28.6
59 TS dt 0.5 time 29.1
60 TS dt 0.5 time 29.6
61 TS dt 0.5 time 30.1
0 TS dt 0.1 time 0.
1 TS dt 0.5 time 0.1
2 TS dt 0.5 time 0.6
3 TS dt 0.5 time 1.1
4 TS dt 0.5 time 1.6
5 TS dt 0.5 time 2.1
6 TS dt 0.5 time 2.6
7 TS dt 0.5 time 3.1
8 TS dt 0.5 time 3.6
9 TS dt 0.5 time 4.1
10 TS dt 0.5 time 4.6
11 TS dt 0.5 time 5.1
12 TS dt 0.5 time 5.6
13 TS dt 0.5 time 6.1
14 TS dt 0.5 time 6.6
15 TS dt 0.5 time 7.1
16 TS dt 0.5 time 7.6
17 TS dt 0.5 time 8.1
18 TS dt 0.5 time 8.6
19 TS dt 0.5 time 9.1
20 TS dt 0.5 time 9.6
21 TS dt 0.5 time 10.1
22 TS dt 0.5 time 10.6
23 TS dt 0.5 time 11.1
24 TS dt 0.5 time 11.6
25 TS dt 0.5 time 12.1
26 TS dt 0.5 time 12.6
TSEvent: Event 0 zero crossing at time 13.1 located in 0 iterations
Ball hit the ground at t = 13.10 seconds
27 TS dt 0.5 time 13.1
28 TS dt 0.5 time 13.6
29 TS dt 0.5 time 14.1
30 TS dt 0.5 time 14.6
31 TS dt 0.5 time 15.1
32 TS dt 0.5 time 15.6
33 TS dt 0.5 time 16.1
34 TS dt 0.5 time 16.6
35 TS dt 0.5 time 17.1
36 TS dt 0.5 time 17.6
37 TS dt 0.5 time 18.1
38 TS dt 0.5 time 18.6
39 TS dt 0.5 time 19.1
40 TS dt 0.5 time 19.6
41 TS dt 0.5 time 20.1
42 TS dt 0.5 time 20.6
43 TS dt 0.5 time 21.1
44 TS dt 0.5 time 21.6
45 TS dt 0.5 time 22.1
46 TS dt 0.5 time 22.6
47 TS dt 0.5 time 23.1
TSEvent: Event 0 zero crossing at time 23.6 located in 0 iterations
Ball hit the ground at t = 23.60 seconds
48 TS dt 0.5 time 23.6
49 TS dt 0.5 time 24.1
50 TS dt 0.5 time 24.6
51 TS dt 0.5 time 25.1
52 TS dt 0.5 time 25.6
53 TS dt 0.5 time 26.1
TSEvent: Event 0 zero crossing at time 26.6 located in 0 iterations
Ball hit the ground at t = 26.60 seconds
54 TS dt 0.5 time 26.6
55 TS dt 0.5 time 27.1
56 TS dt 0.5 time 27.6
57 TS dt 0.5 time 28.1
58 TS dt 0.5 time 28.6
59 TS dt 0.5 time 29.1
60 TS dt 0.5 time 29.6
61 TS dt 0. time 30.1

I don't see the 0.001 timestep here, do you get a different behavior?

Thank you,

Sophie
________________________________
From: Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>>
Sent: Tuesday, October 27, 2020 15:34
To: Blondel, Sophie <sblondel at utk.edu<mailto:sblondel at utk.edu>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>>; xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net> <xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net>>
Subject: Re: [petsc-users] TSSetEventHandler and TSSetPostEventIntervalStep

[External Email]

On Tue, Oct 27, 2020 at 3:09 PM Blondel, Sophie via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:
Hi,

I am currently using TSSetEventHandler in my code to detect a random event where the solution vector gets modified during the event. Ideally, after the event happens I want the solver to use a much smaller timestep using TSSetPostEventIntervalStep. However, when I use TSSetPostEventIntervalStep the solver doesn't use the set value. I managed to reproduce the behavior by modifying ex40.c as attached.

 I stepped through ex40, and it does indeed change the timestep to 0.001. Can you be more specific, perhaps with monitors, about what you think is wrong?

  Thanks,

     Matt

I think the issue is related to the fact that the fvalue is not technically "approaching" 0 with a random event, it is more of a step function instead. Do you have any recommendation on how to implement the behavior I'm looking for? Let me know if I can provide additional information.

Best,

Sophie

--
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.cse.buffalo.edu/~knepley/>

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