[SciPy-User] leastsq (probably simple) question

josef.pktd@gmai... josef.pktd@gmai...
Mon Feb 25 09:50:41 CST 2013


On Sun, Feb 24, 2013 at 9:40 PM, Kevin Gullikson
<kevin.gullikson@gmail.com> wrote:
> Hey all,
>
> I am trying to use scipy.optimize.leastsq to do a one-parameter fit. The
> final result is not very sensitive to the exact value, so I am wondering how
> you can limit leastsq to stop iterating once the values it is testing are
> reasonably close together? Example output from my code:
>
> Resolution-fitting X^2 =  1056.95654172 at R =  [ 51908.71176496]
> Resolution-fitting X^2 =  1054.42705462 at R =  [ 51908.71170349]
> Resolution-fitting X^2 =  1054.42705427 at R =  [ 51908.71174447]
> Resolution-fitting X^2 =  1056.95654172 at R =  [ 51908.71176496]
> Resolution-fitting X^2 =  1056.95654172 at R =  [ 51908.71176496]
> Resolution-fitting X^2 =  1054.42705436 at R =  [ 51908.71173423]
> Resolution-fitting X^2 =  1056.95654181 at R =  [ 51908.71175472]
> Resolution-fitting X^2 =  1054.42705431 at R =  [ 51908.71173935]
> Resolution-fitting X^2 =  1054.42705427 at R =  [ 51908.71174447]
> Resolution-fitting X^2 =  1054.42705427 at R =  [ 51908.71174447]
> Resolution-fitting X^2 =  1054.42705427 at R =  [ 51908.71174447]
> Resolution-fitting X^2 =  3408043.11138 at R =  [ 216058.47126214]
> Resolution-fitting X^2 =  1054.8705442 at R =  [ 51857.89239384]
> Resolution-fitting X^2 =  1054.64687339 at R =  [ 51883.47239909]
> Resolution-fitting X^2 =  1054.53612148 at R =  [ 51896.17634439]
> Resolution-fitting X^2 =  1054.48119765 at R =  [ 51902.48582026]
> Resolution-fitting X^2 =  1054.4539391 at R =  [ 51905.61951157]
> Resolution-fitting X^2 =  1054.44040558 at R =  [ 51907.1759188]
> Resolution-fitting X^2 =  1054.4336851 at R =  [ 51907.9489416]
> Resolution-fitting X^2 =  1054.43034753 at R =  [ 51908.33288072]
> Resolution-fitting X^2 =  1054.42868992 at R =  [ 51908.52357292]
> Resolution-fitting X^2 =  1054.42786665 at R =  [ 51908.61828465]
> Resolution-fitting X^2 =  1054.42745775 at R =  [ 51908.66532545]
> Resolution-fitting X^2 =  1054.42725467 at R =  [ 51908.68868937]
> Resolution-fitting X^2 =  1054.4271538 at R =  [ 51908.70029361]
> Resolution-fitting X^2 =  1054.4271037 at R =  [ 51908.70605713]
> Resolution-fitting X^2 =  1054.42707882 at R =  [ 51908.70891972]
> Resolution-fitting X^2 =  1054.42706646 at R =  [ 51908.71034149]
>
> The parameter I am adjusting is R (the resolution of a spectrograph), and as
> you can see it is doing these tiny changes which have very little affect on
> the X^2 value (that is not reduced X^2, so don't worry that it isn't near
> 1!)
>
> Is there a way to tell leastsq to stop once it gets to say 51908 (in this
> example)?

rescale your function and/or parameters or reduce xtol and ftol
1e-8 will be too small if your values are large

Josef

>
> Kevin Gullikson
>
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