Hi Danny! On Mon, Dec 29, 2008 at 4:01 PM, Danny Tarlow <dannytar...@gmail.com> wrote: [...] >> Is this possible to do with Sympy? If I were interested in working on >> something like this, how hard would it be for a sympy newbie (but >> competent programmer) to implement? Any tips on where to start?
Thanks for both your emails. You need to use the Sum class for that, and I think it will probably need a little enhancements so that everything runs smoothly. I think it should be pretty easy for you to get going with sympy, it's our aim to have the code hackable, so that people can take it and customize it for their needs and enhance it to get the job done. I suggest you learn git, just a few commands are enough, see our tutorial: http://docs.sympy.org/sympy-patches-tutorial.html feel free to ask any question if you don't understand something in the sources. You can also come to #sympy at freenode to chat in live. > For concreteness, here is an example of one of my attempts: [...] > The output is a mess: > mu := [tau_0/5 + tau_1/5 + tau_2/5 + tau_3/5 + tau_4/5] > sigma := [2*mu*tau_0 + 2*mu*tau_1 + 2*mu*tau_2 + 2*mu*tau_3 + > 2*mu*tau_4 - tau_0**2 - tau_1**2 - tau_2**2 - tau_3**2 - tau_4**2 - > 5*mu**2] > tau_0 := [mu] > > Ideally, I'd like to get something more like this, where the sums are > left in tact: > mu := 1/5 * \sum_{i=0}^4 tau_i > sigma := 1/5 * \sum_{i=0}^4 (mu - tau_i) ** 2 > tau_0 := [mu] I see. You need to keep things in the Sum class, unfortunately the docstring of it is not so much helpful (it can be your first patch if you want:), but read it's tests here: sympy/concrete/tests/test_sums_products.py to get dozens of examples of usage. E.g.: In [3]: Sum(1/k**k, (k, 1, oo)) Out[3]: Sum(k**(-k), (k, 1, oo)) In your case probably more something like this: In [4]: Sum(1/k**k, (k, 1, 5)) Out[4]: Sum(k**(-k), (k, 1, 5)) In [5]: Sum(1/k**k, (k, 1, 5)).doit() Out[5]: 27891287 ──────── 21600000 E.g. you don't want to call the "doit()" function. Please report everything that isn't working with the Sum into our issues. If things are easy to fix, I'll fix it myself, if it takes more time, I'll help you fix it. > > For extra credit, there would also be a way to substitute sufficient > statistics for the \sum_{i=0}^4 tau_i terms, for example, so that the > sample mean could be computed once, then used many times in the > updates. the .subs() method should do that. > > Thanks in advance. 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 -~----------~----~----~----~------~----~------~--~---
