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ode and time discrete solver---week-end musing and learning
Posted Oct 16, 2010, 8:41 a.m. EDT Studies & Solvers Version 4.0a, Version 4.1, Version 4.2, Version 4.2a 4 Replies
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No matter what I do [ using bdf, prev operators as explained in the doc or in the exem-le pubished by Nicklas on this forum... I ALWAYS end with duplicate variable errors and some strange variable list in the equation vie mode
for exemple if I try to solve f1'=1, f1(0)=0
I will write in the ode node
bdf(f1,1)-11 as the equation
and put the proper initial condition
I get duplicate variable error names when I try to run
but then in the comsol generated equation some "strange variable are created f1t=bdf(f1,2) GENERATED by comsol and then
f1tt=bdf(bdf(f1,2),1)) again COMSOL generated .... and apparently wrong [ derivative shoud be first order bdf according to the doc...
Does somebody know the proper way to code global ODE for use of discrete time solver?
Or is there a bug/limitation I have not seen in the doc/release note...
I should say that I have no problem coding pde... ONLY global ODE...
I attach the small file corresponding to the little example above
Thanks
JF
EDIT I should add that the SAME coding as above BUT as a weak pde defined on a point on a geometry solve properly the equationbut then I need to export the solution in the glibal settting... complicated
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It's probably a bug in 4.0a (0.993) as in my provisional 4.1 (0.74) your model loads in and solves straight out, no reference to any errors
--
Good luck
Ivar
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this is very helpful
Who do you need to bribe to get a provisionnal. 4.1.? :-)
JF
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Thanks Ivar for your help. I confirm that the model is now running well on 4.1/4.2.
However, I found a new bug:
It seems that if you change the STUDY TYPE from time-dependent to time-discrete (and still keep the time-discrete solver), the error related to 'Duplicate variable names' appears again (see mph file attached).
Hope this bug will be removed in future releases.
Regards,
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