Doesn't expr.equals also do something similar to this? Aaron Meurer
On Mon, Feb 9, 2015 at 1:42 PM, Ondřej Čertík <ondrej.cer...@gmail.com> wrote: > On Mon, Feb 9, 2015 at 12:40 PM, Ondřej Čertík <ondrej.cer...@gmail.com> > wrote: >> Hi Peter, >> >> On Mon, Feb 9, 2015 at 9:09 AM, Peter Chervenski <spoo...@abv.bg> wrote: >>> I made this function to test for the equivalence of two expressions. It >>> doesn't really prove anything, but if the tests are many, the probability of >>> it being wrong becomes negligible. Do such utility functions have a place in >>> SymPy? >>> >>> def equiv(a, b, ntests=15): >>> """ Test if expression a is equivalent to b >>> by comparing the results of many random numeric tests """ >>> >>> # get the symbols >>> sb_a = filter(lambda x: x.is_Symbol, a.atoms()) >>> sb_b = filter(lambda x: x.is_Symbol, b.atoms()) >>> >>> sb = list(set(sb_a + sb_b)) >>> >>> eq = True >>> for i in xrange(ntests): >>> k = dict(zip(sb, np.random.randn(len(sb)))) >>> >>> r_a = a.subs( k ) >>> r_b = b.subs( k ) >>> >>> # prove there is a difference >>> if (r_a - r_b)**2 > 1e-30: # not the same? the expressions are >>> different >>> eq = False >>> break >>> >>> return eq >> >> >> Absolutely. I've also implemented a similar function in one PR: >> >> https://github.com/sympy/sympy/pull/8036/files?diff=unified#diff-2c9ef1ef2c82f5d5781d0d12e1fe4910R33 >> >> It was pointed out to me that we have similar machinery here already: >> >> https://github.com/sympy/sympy/blob/master/sympy/utilities/randtest.py#L43 >> >> This should be unified and put into sympy. We can call it >> "zero_numerical" or something like that ("test_numerically", ...). >> Mathematica calls this PossibleZeroQ (though I think it does both >> symbolic an numerical tests). >> >> Look at the implementation in my PR --- you should allow the user to >> specify the range (I call it [a, b]) as well as the precision. I think >> we can perhaps just test for 0, and then your "equiv" can just call >> this zero testing function for a-b. > > Actually, in my implementation I choose random integers from [-a, a] > and then test an interval > [-a/b, a/b]. That way you will get rational numbers, as opposed to > only integers (that could hide differences). > > Ondrej > > -- > 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 sympy+unsubscr...@googlegroups.com. > To post to this group, send email to sympy@googlegroups.com. > 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/CADDwiVDnybsk6Ke-ocGoPd%2BuB_S7v%3DDCeSgvGTR1JFTXiw5F_g%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 sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. 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%3D6JV%3D_umM9hOnn446tz7Hz3bAL2g1%2B7TuqhYbdG1hmTCGg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
