Thanks for the answers. I do not think I'm wrong when pointing to numerical issues, instead of only the formal ones. A lot of people do not know the floating points : if you do not know than 1.0/3 is not the same thing that 1/3, you can go in big troubles. I will not say that SageMath is guilty but that when numerical calculations are done, you have to be careful, and SageMath gives RIF than can be useful instead of RField.
I will look at Wilinson's polynomial and rootfinding, but I'm also interested in a link to bugs, and in results which are more fundamental to the way the software works (like floating point precision loss). Christophe BAL 2014-10-31 0:04 GMT+01:00 Richard Fateman <[email protected]>: > > > On Wednesday, October 29, 2014 3:38:47 AM UTC-7, Christophe Bal wrote: >> >> Hello. >> >> I'm writing a french book about SageMathCloud and I'm looking for known >> wrong results given by Sage or Sympy due to floats calculations, or due to >> the formal method used. Do you know such things ? My idea is to show to new >> user that a CAS or a numerical tool is not Math God. >> > > Numerical calculation via SageMathCloud is certainly the wrong place to > look. As Gupta points out, numerical error happens rather independent of > that. > > How would you react if I said... > > I'm writing an English book about French mille-feuille pastries and would > like to know about food poisoning. My idea is to show that you can die > from desserts. > > In reality, I think you should have some very simple examples that > distinguish between exact computation and (unstable) numerical calculation. > The classic one is Wilkinson's polynomial and rootfinding. > > > > >> >> I've already posted this question on the Sage list without a lot of >> success. >> >> Christophe BAL >> > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/c7190e1f-9677-4008-a949-30185b8b30e4%40googlegroups.com > <https://groups.google.com/d/msgid/sympy/c7190e1f-9677-4008-a949-30185b8b30e4%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAAb4jGkw1KWYTDWcHT7keGqmWY3cMu-2%3D0hfuX_MbZpm%2B0C9AA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
