Docs for L-BFGS-B mention non-existent parameter

[rmcgibbo]

The documentation for _minimize_lbfgsb, and scipy.optimize.show_options('minimize', 'l-bfgs-b') mention the parameter factr, which is actually not a parameter that the function lets you set.

https://github.com/scipy/scipy/blob/master/scipy/optimize/lbfgsb.py#L216-L222

[larsmans]

Indeed. Also, the code is doing something fishy: fmin_l_bfgs_b sets

ftol = factr * np.finfo(float).eps

then calls _minimize_lbfgsb with this ftol, which in turn does

factr = ftol / np.finfo(float).eps

Looks rather wasteful to me. ftol is not actually used except to derive factr.

[pv]

@larsmans: the reason for that is to make ftol have uniform meaning across solvers. fmin_l_bfgs_b is the old interface function, should be considered deprecated.

[rmcgibbo]

I wrote a small checker that goes through callables and looks for mismatches between the docstrings (parsed with numpydoc) and signatures, and found a few other issues as well. I'll open a separate issue for them all together.

https://github.com/rmcgibbo/doccheck

[rgommers]

@rmcgibbo nice! Your checker might find a home in the scipy repo under tools/. I added a similar checker there a while ago to find missing objects in the html docs (refguide_check.py).

[jllanfranchi]

Related and/or duplicated issues #5231 and #7121. See PR #7252 to update the docs.