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Time-step chosen by BDF method?

Posted Apr 28, 2011, 10:07 a.m. EDT Studies & Solvers 2 Replies

Guillermo Vilaplana
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Hi,

The time-dependent solver chooses an extremely small time-step, and I can't find how this time-step is chosen.

Any guess?

All what I found is :
"IDA [...] uses variable-order variable-step-size backward differentiation formulas (BDF)."
p 365 Reference Guide


Thank you very much for your help.
Guillermo Vilaplana
2 Replies Last Post Apr 28, 2011, 4:25 p.m. EDT
Gabriel Caron
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Posted: 1 decade ago Apr 28, 2011, 3:16 p.m. EDT
If you want to controle it instead:

Under Study ->SolverConfiguration -> Solver x -> Time-Dependent solver x

Time Stepping Tab.
If you want to controle it instead: Under Study ->SolverConfiguration -> Solver x -> Time-Dependent solver x Time Stepping Tab.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 28, 2011, 4:25 p.m. EDT
Hi

The time stepper often starts with small steps, as often we are lazy and leave "0" as initial conditions, but true current, or heat flux starting far away from "0" so the system believes its facing a large derivative at the beginning of the transient solver sequence, hence small steps. use better initial conditions with smooth transitions and your solver will converge quicker

--
Good luck
Ivar
Hi The time stepper often starts with small steps, as often we are lazy and leave "0" as initial conditions, but true current, or heat flux starting far away from "0" so the system believes its facing a large derivative at the beginning of the transient solver sequence, hence small steps. use better initial conditions with smooth transitions and your solver will converge quicker -- Good luck Ivar

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