Am 26.10.2010 12:38, schrieb josef.p...@gmail.com: > On Tue, Oct 26, 2010 at 3:28 PM, Pauli Virtanen<p...@iki.fi> wrote: >> Tue, 26 Oct 2010 12:16:53 -0700, Nicolai Heitz wrote: >>> I am not sure if you are the right persons to contact but if not I would >>> appreciate a short notice and maybe an address where I can find help. I >>> already posted this this message in an other python mailing list and >>> they forwarded me to this list and told me that I might find help here. >> Some comments: >> >> 1) General advice: When doing numerics, it's generally a good idea to use >> units natural for the problem, and not SI ones. The numbers the computer >> sees should be of order 1. Not all numerical algorithms are scale >> invariant. > I also think it will be difficult to get good numbers by numerical > differenttiation with this scaling. > I knew before that the scaling might causes some problems but I didn't expect them to arise on that level. I thought numdifftools should be robust in those typical physical units/scales. I can transform it into natural units but this is not the best solution and I still hope for somebody to come up with a solution for SI units. >> 2) The scipy-user list might be even more appropriate: >> >> http://mail.scipy.org/mailman/listinfo/scipy-user I contacted them already but they didn't responded so far and I was forwarded to that list which was supposed to be more appropriated. >> 3) The numdifftools authors might be more knowledgeable about their >> software: >> >> http://code.google.com/p/numdifftools/ >> >> If you are sure it's a bug in numdifftools, click the issues tab and >> write a report. Be sure to include simple test case (like the one you >> attached). > Per might be reading this or scipy-user. > > My guess would be that it is not a bug but numerical precision > problems in a difficult use case. The question is however useful, > because I haven't seen much discussion yet about a robust use of > numdifftools. > > Josef > I am not sure if it is a bug either. I mean for most of the numbers I tested the code (not having a magnitude of e-28) like 2.5, 1, 1e-10 numdifftools works all fine. My question is more like
1) Can I make it run/fix it, so that it is also going to work for the SI scaling? 2) How can I be sure that increasing the number of ions or adding a somehow more complicated term to the potential energy is not causing the same problems even in natural units? 3) In which range is numdifftools working properly. Nicolai >> -- >> Pauli Virtanen >> >> _______________________________________________ >> NumPy-Discussion mailing list >> NumPy-Discussion@scipy.org >> http://mail.scipy.org/mailman/listinfo/numpy-discussion >> > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion