Re: limitations of fit?

[Hans-Bernhard B. <HBB...@t-...>]

Am 31.01.2015 um 20:47 schrieb pl...@pi...:

> I have about 2300 data points that I need to fit a simple cosine to.
> However, fit says it is converging at the first iteration and
> effectively does nothing.
>
> The data has a good signal to noise and I have primed the parameters
> with values which are pretty close. It just needs to shift the constant
> term closer to zero.

The RMS you got appears to disagree with that assessment.

 > final sum of squares of residuals : 3036.32

For 2300 points, and a function that only varies between 0 and 2 with 
the given starting parameters, you're getting an average deviation 
between function and data of more than 1.0 per data point.  That's quite 
a bit removed from being "pretty close".

> I had this working fine with less data points (about 200)  on
> essentially the same dataset.

200 data points cannot ever be "essentially the same dataset" as 2300.

> Is the large number of points causing fit to fail to converge properly?

Almost certainly not.

For a more meaningful answer you'll have to divulge the dataset in question.