[SciPy-user] RE : Re: help on numerical modelisation of near-sinusoidal function using SciPy for pendulum analysis

Robert VERGNES robert.vergnes at yahoo.fr
Fri Dec 8 01:34:54 CST 2006


Thanx for your help.
Robert

Travis Oliphant <oliphant at ee.byu.edu> a écrit : palazzol at comcast.net wrote:

>Hi,
>
>I think optimize.minpack.leastsq() could be made to work, but it would be best if you could make good initial guesses for a,b,co, and phi.   You could use some ad-hoc methods to come up with guesses for these initial conditions, based on looking at a bit of the waveform, and then use leastsq() to calculate the best values and residual error norm.  For example, a is the average over time, b is the half the amplitude between peaks, co based on Theta(t) crossing a, etc.
>  
>

optimize.leastsq  (don't use the minpack itermediary because that could 
change)   is the function you want for general curve-fitting.  You can 
also use another optimization function with a slightly different function.

This is also similar to the frequency estimation problem so the fft is a 
good fit to get starting estimates as Frank suggests.   A simple 
algorithm could be constructed in a few lines using the fft and 
optimize.leastsq.

-Travis

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