Discussion Forum

Hi

What if you try an indexed search on your doc pdf files, it took me 10 sec to identify "Guide.pdf" and then 10 more to get to page 392 (V3.5a) where there is a chapter devoted to time sequence settings :)

In fact many of the replies on the forum can be found by an indexed search of the doc files, there is a lot of stuff therein, but somtimes its not obvious to locate it ;)

Bonne lecture
Ivar

PS:
Autres choses, on me fait des remarques que nous devons nous efforcer à utiliser l'anglais sur le forum pour faciliter le suivi "mondial"

Ivar,
thank you for your prompt answer
of course I did what you suggeste a long time ago that but I guess I explained myself poorly in my previous post
According to the documentation, the output time step is for OUTPUT ONLY and my question should be trivial
UNFORTUNATELY what I have found is that there is a correlation between the convergence of the solution and the output time specifiec in the time stepping area as explained in p392.
the correlation is seen becasue if I specify a small out put time I get a correct solution BUT a large number of snapshot and if I ask for a small number of snapshot there I get a convergence failure .... which I canot understand based on the documentaito I read in the user guide [ p392 and subsequent...
I also tried to set a manual maximum time step in the time stepping tab equal to the small output time step that provide me with a solution and set a larger time step corresponding to my post processing requirement but then get another failure convergence.
So I believe that my question has merit in the sense that comsol doc [ p392 and subsequent ]APPARENTLY indicates that time stepping ONLY drive times where snapshot are taken but my experience demonstrate APPARENTLY otherwise.

I am sure there is a sublety somewhere but again not found obvjously in the documentation.
jean Francois

ps as for the language comment, I dont see that as a problem with me, even if I answered in french to a quesiton asked in french... but then does that mean this community will defacto exclude non english speaker....?

Hi Jean Francois - Suppose your simulation will run for total_sim_time, with max_time_step set small enough to avoid convergence errors, and you want num_of_snapshots sets of output along the way. Here is a piece of code that I've had success with:

output_time_list = linspace(0, total_sim_time, num_of_snapshots);
fem.sol = femtime(fem, ...
'Maxstep', max_time_step, ...
'Tlist', output_time_list, ...
'Tout', 'Tlist');

Tom

Thanks a lot Thomas.
I will use your suggestion it should apparently solve my conundrum

Hi

Yes, I should have expected that you had read the docs, sorry for that.

For the language issue, keep kool, I reacted too as you and answered in French, I mostly switch language without noticing it, but it's to help keeping the "rules" there basically to allow everyone to follow, more or less.
And I would have serious problems to get anything meaninful out, if the people from the East started to exchange with their language and signs, but a common language, even if difficult for several out there helps to keep a common denominator.

By the way do you know the most spoken language ? ...
No, not chinese, it's "internet english" ;)

Have a nice day
Ivar

Not a problem Ivar
but if Thomas has provided me with a practical fix,[ which mean thatobviously the problem is known...]
I stil would love to understand what is the relationship between time stepping [ defined as per p392 in the user guide in its most basic way] and the way comsol calculates its internal time step when solving a problem.

My reading of the doc is that they should be NO constraining relationship , Comsol doing its stuff and reporting result when asked to do so....but again
I have example that tell me otherwise..
and I usually like to understand what I am doing... :-)

so do you have any clue on that?

As for the language I am very ¨KOOL¨ and use Internet english for myself but i will have no problem if a group of people where choosing another language .. they will just not get as much support as they could expect if they were using english but then it will be their choice...
Have a great day !
JF

Hi Jean-François

Well when I get really stuck and need help, I use COMSOL support, to now they have been very efficient.
But usually I also fight several hours before I ask them, I do not like to not be able to understand by myself (encore ces doubles négations du français qui passent mal en anglais). I can only confirm that there are several domains where the COMSOL jump rather quickly over difficult subjects, often too I believe they search to protect themself from being too obviously copied. COMSOL is shaking up the traditional FEM software industry with their very general and new multiphysics approach.

When you explain well your case the reply from support is just better

Good luck
Ivar

Ivar
thank you for the advice..
duly noted.
btw i feel the same as you do and feel the need to understand what i do ...:-)
I also found a practical way to resolve my initial worry [ slow post processing due to the very large and ünnecessary for post processing¨number of snapshot generated by comsol which is to use interpolated time in the post processing phase of the work and I can extract exactly the snapshot i want . so I learned something in the process lol

Now having say that I still believe the documentation on the solving process is ambiguous and possibly misleading as written on this issue
jf

Hi

by the way have you checked the "mlinterface.pdf", in particular the "FEM.EVENT—EXPLICIT AND IMPLICIT EVENTS" p.46, you might find some usefull info there, its a quick guess. I'm not sure its what you need

Good luck
Ivar