[Scipy-tickets] [SciPy] #1542: fmin_bfgs gets stuck in an infinite loop when parameters are NaN

SciPy Trac scipy-tickets@scipy....
Mon Oct 24 07:38:42 CDT 2011

#1542: fmin_bfgs gets stuck in an infinite loop when parameters are NaN
 Reporter:  scipydevwikiaccount  |       Owner:  somebody   
     Type:  defect               |      Status:  new        
 Priority:  normal               |   Milestone:  Unscheduled
Component:  scipy.optimize       |     Version:  devel      
 Keywords:                       |  
 I have a problem where scipy's fmin_bfgs function will get stuck in an
 infite loop when one of the parameters is NaN. The reason this concerns me
 is that for some reason, the fitter in my code is pushing parameters to be
 NaN and then gets stuck in the loop.

 Unfortunatly, I am unable to reproduce the more important issue of
 parameters getting set to NaN, but having the code finish would be a step
 in the right direction!

  I do have a very simple example where scipy gets stuck in this infinite
 loop when the starting value is NaN.

 import numpy as np
 from scipy import optimize

 f=lambda x: x
 x0 = [np.nan]

 print 'fmin works',optimize.fmin(f, x0, disp=False, maxiter=10)

 fp=lambda x: np.ones_like(x)
 print 'fmin_bfgs gets stuck in a loop',optimize.fmin_bfgs(f, x0, fp,
 disp=False, maxiter=10)

 The reason this happens is that the functions line_search_wolfe1 and
 line_search_wolfe2 have 'while 1' loops which never break when the fit
 parmaeters are nan. So my suggested fix is to add an explicit check to
 these functions that breaks in the case that these paramters are nan.

 Thanks in advance,

Ticket URL: <http://projects.scipy.org/scipy/ticket/1542>
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