On Sat, May 16, 2009 at 1:50 AM, Vinzent Steinberg <vinzent.steinb...@googlemail.com> wrote: > > On May 15, 9:04 pm, Ondrej Certik <ond...@certik.cz> wrote: >> <vinzent.steinb...@googlemail.com> wrote: >> > Please note that you also could use the brand-new nsolve() to do this >> > without calling mpmath directly and using a simpler syntax. (If besselj >> > () was implemented in sympy.) >> >> > By the way, nsolve() should support scipy too. Do you think it should >> > be implemented in nsolve() or in mpmath's findroot()? >> >> If there is a way to take advantage of symbolic stuff, then in sympy, >> if it's just pure numerics, then mpmath is fine too. > > Yeah, but in this case it would simplify the code, because you would > not need all the lambdas.
If you are referring to the code above in this thread, then I don't use it in the patches sent to sympy-patches anymore. I think I only one lambda, but that's necessary. > >> >> Btw, how is it possible that findroot returns complex numbers >> sometimes? E.g. I had to do the following hacks: >> >> + if method == "sympy": >> + # The findroot() is fragile, it sometimes returns complex >> numbers, >> + # so we chop all complex parts (that are small anyway). Also we >> + # need to set the tolerance, as it sometimes fail without it. >> + def f_real(x): >> + return f(complex(x).real) >> + root = findroot(f_real, x, solver="muller", tol=1e-9) >> + root = complex(root).real > > Why are you using method='muller'? This method is known for converging > towards complex roots even with real starting points! It's not > "fragile", it's actually an expected behavior. See the docstring [1]. It's the only method that converges... I can of course just write my own netwon method, but I hoped to use something that we have already. > >> >> Which is not nice. Also I had to setup tol=1e-9, otherwise the >> doctests run when executed directly, but fail when executed using >> ./setup test (e.g. after running the regular testsuite), so it looks >> like there is some global state in findroot. > > This is an general issue of mpmath, you need to set explicitly mp.dps > = 15 at the beginning of every doctest, because if a doctest that > changes dps is executed before, you might get a precision you did not > expect. Well, that's a serious problem. > > Currently mp is being made context-dependent rather than global. Excellent. > >> >> Compare this to scipy: >> >> + elif method == "scipy": >> + root = newton(f, x) >> >> it just works. It can be a problem in evaluating the jn() function, >> since in the sympy case, I am using the sin/cos representation, while >> in the scipy case I am just calling sph_jn() from scipy. >> >> Ondrej > > root = findroot(f, x) should just work too. Unfortunately it doesn't. 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 -~----------~----~----~----~------~----~------~--~---
