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Parametric Sweep gives different results with separate calculations

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Hello,

Strange things happened when I use Parametric sweep function today. Initially, I solved a model by setting a parameter as a fixed number ( say "a"). Then I swept this parameters with different values (say "a", "b" , and 'c"). Both calculations converged but when I checked the results, the one from separate calculation ("a" only), is different from the one (with same parameter value "a") obtained from parametric sweep.
I checked several times and redid the modeling for couple of times, but do know the reasons.

Someone also encountered similar problems? Which results should I trust and what might be the reason?
Please advice,
Thanks!

1 Reply Last Post Jul 14, 2014, 7:06 a.m. EDT
Frank van Gool COMSOL Employee

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Posted: 1 decade ago Jul 14, 2014, 7:06 a.m. EDT
Dear Neverland,

A parametric sweep will typically reuse the previous result as initial conditions for the next parameter. This means that a different solving path is taken.
Next to this, a non-linear problem might have multiple solutions which are all valid. Depending on the initial conditions you can find a different result. (for instance different flow profiles can be found in a CFD model)

Maybe you can elaborate a bit on what type of difference we are looking at. Do you have a different magnitude of the solution (by how much), or do you have a different shape of the solution?

If the magnitude is highly different, you might want to check the results with a lower relative tolerance (say 1e-5 vs. 1e-3) and recheck the results.

If the shape is different, I typically rely more on the sweep results as this often follows a natural path.

Note that if you do not want to reuse the previous results, uncheck "use parametric solver" in the parametric sweep.

Best regards,
Frank
Dear Neverland, A parametric sweep will typically reuse the previous result as initial conditions for the next parameter. This means that a different solving path is taken. Next to this, a non-linear problem might have multiple solutions which are all valid. Depending on the initial conditions you can find a different result. (for instance different flow profiles can be found in a CFD model) Maybe you can elaborate a bit on what type of difference we are looking at. Do you have a different magnitude of the solution (by how much), or do you have a different shape of the solution? If the magnitude is highly different, you might want to check the results with a lower relative tolerance (say 1e-5 vs. 1e-3) and recheck the results. If the shape is different, I typically rely more on the sweep results as this often follows a natural path. Note that if you do not want to reuse the previous results, uncheck "use parametric solver" in the parametric sweep. Best regards, Frank

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