When chop=True it uses the current precision to replace small arguments with an exact zero. If you want to specify the threshold for chopping, pass in a value instead of a boolean. The exp(-60) is about 8x10^-27 so if you specify chop smaller than that you will not get 0 for the result:
>>> expr.n(chop=1e-27) 0.482830727370613 >>> expr.n(chop=1e-26) 0 On Thursday, May 21, 2015 at 1:49:34 PM UTC-5, Paul Royik wrote: > > OK. > Thank you. > Could you move it to issues? > > On Thursday, May 21, 2015 at 6:45:41 PM UTC+3, Aaron Meurer wrote: >> >> I'm guessing chop chops some intermediate expression that is smaller >> than the cutoff in this case. It probably should be considered a bug. >> >> Aaron Meurer >> >> On Thu, May 21, 2015 at 8:53 AM, Paul Royik <[email protected]> wrote: >> > Nobody could tell how chop works? >> > >> > On Tuesday, May 5, 2015 at 11:41:24 AM UTC+3, Paul Royik wrote: >> >> >> >> expr = >> >> >> 2682469501914725726236807146020965585039500052171867725591732162347*exp(-60)/48648670709168952944186714683693506574127 >> >> >> >> >> >> N(expr) outputs 0.482830727370627 >> >> but >> >> N(expr, chop=True) outputs 0 >> >> >> >> In some other expressions chop doesn't make 0. >> >> >> >> So, how chop works? >> > >> > -- >> > 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/3ef42fe1-b3cb-45d3-80ef-6af88a181bb2%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/27ffc6c5-bd6f-4eb3-86fb-1810f01fbe57%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
