I definitely like this example ! Christophe BAL
2014-10-31 17:33 GMT+01:00 Aaron Meurer <[email protected]>: > Here is a nice example > https://groups.google.com/d/msg/sympy/YpV5tyLvWe4/WWRYOTMNIhIJ. It > shows great precision loss when evaluating Legendre polynomials > naively. Unlike Wilkinson's polynomial, Legendre polynomials are a bit > more "real-life", and someone solving real problems could definitely > run into this issue if they aren't careful. > > Aaron Meurer > > On Fri, Oct 31, 2014 at 6:15 AM, Christophe Bal <[email protected]> > wrote: > > 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 > . > >> > >> 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. > > -- > 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/CAKgW%3D6J24tuwZujZYzo3AnszQBh6-dN0jJ3PE%3D7Le9q2U-e1XA%40mail.gmail.com > . > 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/CAAb4jG%3Df%3DCE3ccrz%2BP6xCMirPS0M_CJSR3fumOaVmHu%3DM9yDYA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
