问题
I am trying to fit 3 peaks using lmfit with a skewed-Voigt profile (this is not that important for my question). I want to set a constraint on the peaks centers of the form:
peak1 = SkewedVoigtModel(prefix='sv1_')
pars.update(peak1.make_params())
pars['sv1_center'].set(x)
peak2 = SkewedVoigtModel(prefix='sv2_')
pars.update(peak2.make_params())
pars['sv2_center'].set(1000+x)
peak3 = SkewedVoigtModel(prefix='sv3_')
pars.update(peak3.make_params())
pars['sv3_center'].set(2000+x)
Basically I want them to be 1000 apart from each other, but I need to fit for the actual shift, x. I know that I can force some parameters to be equal using pars['sv2_center'].set(expr='sv1_center'), but what I would need is pars['sv2_center'].set(expr='sv1_center'+1000) (which doesn't work just like that). How can I achieve what I need? Thank you!
回答1:
Just do:
pars['sv2_center'].set(expr='sv1_center+1000')
pars['sv3_center'].set(expr='sv1_center+2000')
The constraint expression is a Python expression that will be evaluated every time the constrained parameter needs to get its value.
来源：https://stackoverflow.com/questions/61182584/constraint-on-parameters-in-lmfit