Looking for a nonlinear equation with the following property

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SUMMARY

The discussion centers on finding a nonlinear equation that approximates a sigmoid curve, specifically for ecological modeling. The user initially attempted to use the logistic equation, represented as 1/(1*e^(-a)) * 1/(1*e^(-b)), but found that applying the logit link resulted in ln(e^a + e^b + e^(a+b)), which does not yield a linear function of parameters a and b. The suggestion provided was to utilize piecewise linear functions as an alternative approach.

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Ecologists, mathematicians, and data scientists interested in modeling nonlinear relationships, particularly those seeking to apply sigmoid functions in their analyses.

wvguy8258
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Hi,

I am looking for a nonlinear equation capable of approximating a sigmoid curve that can be multiplied by another equation of the same type with different parameters and this product can be made linear in the parameters. I am an ecologist, so I hope I am using the right terms. I originally tried this with the logistic equation.

1/(1*e^(-a)) * 1/(1*e^(-b))

after applying the logit link to this you end up with

ln (e^a + e^b + e^(a+b))

which won't work for my purposes. I need to end up with a linear function of a and b. Any ideas on equations to try out?

seth
 
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You can approximate them with piecewise linear functions.
 

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