Damping parameter tau for parameter optimization

[cjwang]

I am working on a multi-parameter optimization problem and have some instability issues (large parameter jumps that lead to errors in forward FE). In the user manual, I noticed I can customize the damping parameter tau to better control the stepping sizes. What is the correct way to implement it? Is it the same with the <scale_parameters> command in the options section?

Thanks in advance.

[maas]

Hi,

You can set the "tau" parameter in the Options section. For instance,

    <Options type="constrained levmar">
        <obj_tol>0.001</obj_tol>
        <f_diff_scale>0.001</f_diff_scale>
        <tau>1e-3</tau>
    </Options>

To be honest, I'm not exactly sure how it will affect the optimization. Another strategy if you see these big jumps, might be to find different starting values, since your current values might be too far from the solution. Hope this helps!

Best,

Steve

[cjwang]

Thanks, Steve. Is 1e-3 the default initial value for the tau parameter?

[maas]

Yes, 1e-3 is the default value used for tau in FEBio.

Best,

Steve