[SciPy-User] Fwd: fmin_bfgs stuck in infinite loop

josef.pktd@gmai... josef.pktd@gmai...
Mon Oct 24 14:59:10 CDT 2011


tricky things these reply to all, forwarding to list

---------- Forwarded message ----------
From:  <josef.pktd@gmail.com>
Date: Mon, Oct 24, 2011 at 3:52 PM
Subject: Re: [SciPy-User] fmin_bfgs stuck in infinite loop
To: johann.cohen-tanugi@lupm.in2p3.fr


On Mon, Oct 24, 2011 at 3:43 PM, Johann Cohen-Tanugi
<johann.cohen-tanugi@lupm.univ-montp2.fr> wrote:
> indeed, see the email I just sent : for nan linesearch_wolfe1 does not exit
> gracefully, so that Ralf's patch is never encountered.

I'm not sure what's going on,

I just copied the few lines from
https://github.com/scipy/scipy/commit/a31acbf into my scipy 0.9 and
the original example stops and I'm not able to produce an endless loop
anymore when I try to change around with any of the examples, even
when I start with a nan, it stops immediately.  I only tried the one
parameter example.

Can you check that you actually run the code that has this fix?

Josef


> Johann
>
> On 10/24/2011 09:26 PM, josef.pktd@gmail.com wrote:
>>
>> On Mon, Oct 24, 2011 at 2:39 PM, Johann Cohen-Tanugi
>> <johann.cohentanugi@gmail.com>  wrote:
>>>
>>> Dear Josef
>>> On 10/24/2011 07:58 PM, josef.pktd@gmail.com wrote:
>>>>
>>>> On Mon, Oct 24, 2011 at 1:56 PM,<josef.pktd@gmail.com>    wrote:
>>>>>
>>>>> On Mon, Oct 24, 2011 at 1:50 PM, Johann Cohen-Tanugi
>>>>> <johann.cohentanugi@gmail.com>    wrote:
>>>>>>
>>>>>> Hello,
>>>>>> the OP is a colleague of mine and I looked quickly at the code. The
>>>>>> infinite
>>>>>> loop in the OP's illustrating script comes from the "while 1" loop in
>>>>>> l.144
>>>>>> of linesearch.py : becuse phi0 is np.nan, phi1 is returned as np.nan
>>>>>> as
>>>>>> well, and the break condition is never met. There is an easy fix :
>>>>>>     while 1:
>>>>>>         stp, phi1, derphi1, task = minpack2.dcsrch(alpha1, phi1,
>>>>>> derphi1,
>>>>>>                                                    c1, c2, xtol, task,
>>>>>>                                                    amin, amax, isave,
>>>>>> dsave)
>>>>>>         if task[:2] == asbytes('FG') and not np.isnan(phi1):
>>>>>>             alpha1 = stp
>>>>>>             phi1 = phi(stp)
>>>>>>             derphi1 = derphi(stp)
>>>>>>         else:
>>>>>>             break
>>>>>>
>>>>>> but it is not a nice kludge.... Is there a better way to secure this
>>>>>> while 1
>>>>>> loop? I am sure I am not covering all possible pathological cases with
>>>>>> adding "not np.isnan(phi1)" in the code above.
>>>>>
>>>>> Is this still a problem with 0.10 ?
>>>>> I thought this fixed it, https://github.com/scipy/scipy/commit/a31acbf
>>>
>>> Well I am a complete newby with github, but I think I went to the head of
>>> master before testing, and the problem is still there. I can see the code
>>> snippet from https://github.com/scipy/scipy/commit/a31acbf in my local
>>> copy,
>>> and this is testing against +/-inf, not nan. Changing the OP's code to
>>> test
>>> against inf yields :
>>> In [1]: run test_bgfs.py
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/optimize.py:303:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  if (max(numpy.ravel(abs(sim[1:] - sim[0])))<= xtol \
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/optimize.py:308:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  xr = (1 + rho)*xbar - rho*sim[-1]
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/optimize.py:350:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  sim[j] = sim[0] + sigma*(sim[j] - sim[0])
>>> fmin works [ inf]
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/linesearch.py:132:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  alpha1 = min(1.0, 1.01*2*(phi0 - old_phi0)/derphi0)
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/linesearch.py:308:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  alpha1 = min(1.0, 1.01*2*(phi0 - old_phi0)/derphi0)
>>>
>>> /home/cohen/sources/python/scipydev/lib/python2.6/site-packages/scipy/optimize/linesearch.py:417:
>>> RuntimeWarning: invalid value encountered in subtract
>>>  B = (fb-D-C*db)/(db*db)
>>> fmin_bfgs gets stuck in a loop [ nan]
>>>
>>> so it looks like your code solves the inf situation, but not the nan.
>>
>> It's not my fix (I'm still on scipy 0.9 and avoid bfgs because I don't
>> want to have to kill my interpreter session)
>>
>> isfinite also checks for nans
>>
>>>>> np.isfinite(np.nan)
>>
>> False
>>
>> so there should be another reason that the linesearch doesn't return.
>>
>> Josef
>>
>>
>>
>>
>>
>>>
>>>> Is http://projects.scipy.org/scipy/ticket/1542 the same?
>>>
>>> yes it looks like a duplicate
>>>>
>>>> josef
>>>>
>>>>> Josef
>>>>>
>>>>>
>>>>>> thoughts?
>>>>>> Johann
>>>>>>
>>>>>> On 08/14/2011 01:38 AM, b9o2jnbm tsd71eam wrote:
>>>>>>
>>>>>> I have run into a frustrating problem where scipy.optimize.fmin_bfgs
>>>>>> will
>>>>>> get stuck in an infinite loop.
>>>>>>
>>>>>> I have submitted a bug report:
>>>>>>
>>>>>> http://projects.scipy.org/scipy/ticket/1494
>>>>>>
>>>>>> but would also like to see if anybody on this list has any suggestions
>>>>>> or
>>>>>> feedback.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> --
>>>>>> This message has been scanned for viruses and
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>>>>>> believed to be clean.
>>>>>>
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>


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