scipy/scipy — pull request #3098 by pv (2013-11-29 18:28:24+00:00)
Title: Specifying absolute errors in curve_fit

Continued from gh-448

An option absolute_sigma is added to scipy.optimize.curve_fit, to accommodate the common cases:

- sigma = relative weights, pcov variance estimated from data
- sigma = one standard deviation errors on ydata, determines pcov variances

Also, make the returned `pcov` always be a 2D array. In indeterminate cases, it used to return a scalar, which may not be desirable.