# [SciPy-User] leastsq (probably simple) question

Kevin Gullikson kevin.gullikson.signup@gmail....
Mon Feb 25 09:56:30 CST 2013

```I have tried playing with xtol and ftol, even pushing them all the way to
10, but it doesn't seem to have any effect.

On Mon, Feb 25, 2013 at 9:50 AM, <josef.pktd@gmail.com> wrote:

> 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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> > SciPy-User@scipy.org
> > http://mail.scipy.org/mailman/listinfo/scipy-user
> >
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