Sigmoid Curve Fitting

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve
to a set of data points?

Regards,
Chris

That question would probably be better asked on the scipy-users list. I believe there is something for that, but I am not familiar with it.

Ben Root

···

On Mon, Sep 20, 2010 at 3:36 PM, Chris Spencer <chrisspen@…1003…7…> wrote:

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve

to a set of data points?

Regards,

Chris

I am very curious to know how this is done. I have seen in many Cloud Condensation Nuclei (CCN) counter calibration experiments [e.g. Rose et. al. (2008) - p1156, fig2 http://www.atmos-chem-phys.net/8/1153/2008/acp-8-1153-2008.html] people use sigmoidal fits. Never seen a code is shared so far or how it is obtained.

from scipy.optimize import leastsq

could be a good point to start. To me this fit is very likely a least square minimization problem. You have your tanh(x) or 1/(1+e^-x) as a sigmoidal function, and you should find the points that will make the error minimal for a given discrete points/measurements.

from scipy.optimize import curve_fit might be another way to approach.

···

On Mon, Sep 20, 2010 at 3:36 PM, Chris Spencer <chrisspen@…287…> wrote:

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve

to a set of data points?

Regards,

Chris


Gökhan

You could also experiment at zunzun.com. Choose 2D sigmoidal from the 2D function scroll list.

···

On Mon, Sep 20, 2010 at 3:36 PM, Chris Spencer <chrisspen@…1003…7…> wrote:

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve

to a set of data points?

Gökhan

Thank you. I'll try investigating Scipy further. I've already tried
applying some least-squares code for Numpy
(http://pingswept.org/2009/01/24/least-squares-polynomial-fitting-in-python/)
to my sigmoid data, but it only seems to fit parabolas.

I had already encountered zunzun.com while Googling the problem. I'm
not sure what to make of it, although it seems to be an online
curve-fitting service. Unfortunately, my usage requires the ability to
run the process locally.

Regards,
Chris

···

On Mon, Sep 20, 2010 at 6:35 PM, Gökhan Sever <gokhansever@...287...> wrote:

On Mon, Sep 20, 2010 at 3:36 PM, Chris Spencer <chrisspen@...287...> wrote:

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve
to a set of data points?

You could also experiment at zunzun.com. Choose 2D sigmoidal from the 2D
function scroll list.
--
Gökhan

Hi,

Scipy.optimize.leastsq finds a least square fit to an arbitrary function. Check the scipy cookbook example: http://www.scipy.org/Cookbook/FittingData

Regards,

Bartosz

···

On 20.09.2010, at 22:36, Chris Spencer wrote:

Hi,

Does Matplotlib/Numpy/Scipy contain the ability to fit a sigmoid curve
to a set of data points?

Regards,
Chris

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Bartosz Telenczuk

Institute for Theoretical Biology
Humboldt University of Berlin
Germany
http://neuroscience.telenczuk.pl