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tBuLi / symfit

Symbolic Fitting; fitting as it should be.
http://symfit.readthedocs.org
MIT License
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Implement ODEmodel in a piecewise manner #301

Closed RebetezG closed 4 years ago

RebetezG commented 4 years ago

I was wondering if there was an easy way to implement ODEmodel in a piecewise manner like:

If t>to: D(A,t) = -k1 A

else: D(A,t) = -k2 A

tBuLi commented 4 years ago

That's an interesting question. I haven't tried this but I believe the following should work:

from symfit import Piecewise, D, parameters, variables

A, t = variables('A, t')
k1, k2 = parameters('k1, k2')
t0 = 5.0
model_dict = {
    D(A, t): Piecewise((- k1 * A, t > t0), (- k2 * A, t <= t0))
}

where Piecewise is a sympy object which can just be imported from symfit like everything else. It is also possible to make t0 into a Parameter as well if that's what you need.

Good luck modeling corona virus outbreaks or whatever it is you're trying to do, and let me know if it works!

RebetezG commented 4 years ago

It works like a charm! Thanks for the quick response and this great package!

tBuLi commented 4 years ago

Excellent! Happy to hear that it worked and that you enjoy the package!