On Thu, Jul 30, 2009 at 5:39 PM, Phillip M. Feldman<pfeld...@verizon.net> wrote: > > When I type something like the following, I would expect to get a > result of oo, indicating that the sum diverges to infinity: > > sum(1/n, (n, 2, oo)) > > Instead, I get the same thing back (actually not quite-- the 's' > changes to a capital 'S'). Any idea why this doesn't work?
This is what I get: In [1]: sum(1/n, (n, 2, oo)) Out[1]: Sum(1/n, (n, 2, oo)) This just returns the Sum instance, meaning, that you can do stuff on it, like: In [2]: a = sum(1/n, (n, 2, oo)) In [3]: a.n() --------------------------------------------------------------------------- ValueError Traceback (most recent call last) /home/ondrej/repos/sympy/<ipython console> in <module>() /home/ondrej/repos/sympy/sympy/core/evalf.pyc in Basic_evalf(x, n, **options) 1006 options['maxprec'] = max(prec, DEFAULT_MAXPREC) 1007 try: -> 1008 result = evalf(x, prec+4, options) 1009 except NotImplementedError: 1010 # Fall back to the ordinary evalf /home/ondrej/repos/sympy/sympy/core/evalf.pyc in evalf(x, prec, options) 946 try: 947 rf = evalf_table[x.func] --> 948 r = rf(x, prec, options) 949 except KeyError: 950 #r = finalize_complex(x._eval_evalf(prec)._mpf_, fzero, prec) /home/ondrej/repos/sympy/sympy/core/evalf.pyc in evalf_sum(expr, prec, options) 854 raise NotImplementedError 855 # Use fast hypergeometric summation if possible --> 856 v = hypsum(func, n, int(a), prec2) 857 delta = prec - fastlog(v) 858 if fastlog(v) < -10: /home/ondrej/repos/sympy/sympy/core/evalf.pyc in hypsum(expr, n, start, prec) 818 raise ValueError("Sum diverges like (%i)^n" % abs(1/g)) 819 if p < 1 or (p == 1 and not alt): --> 820 raise ValueError("Sum diverges like n^%i" % (-p)) 821 # We have polynomial convergence: use Richardson extrapolation 822 # Need to use at least quad precision because a lot of cancellation ValueError: Sum diverges like n^-1 E.g. this tells you that the sum diverges. Maybe the sum could return oo immediately. Ondrej --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy?hl=en -~----------~----~----~----~------~----~------~--~---