I guess solve() uses the inverse method, like In [14]: tan(x).inverse() Out[14]: sympy.functions.elementary.trigonometric.atan
So we just need to define that for erf and erfinv. Aaron Meurer On Mon, Oct 7, 2013 at 11:36 AM, Matthew Rocklin <mrock...@gmail.com> wrote: > Yes, erfinv > > http://docs.sympy.org/dev/modules/functions/special.html#sympy.functions.special.error_functions.erfinv > > > On Sun, Oct 6, 2013 at 10:54 PM, Aaron Meurer <asmeu...@gmail.com> wrote: >> >> >> On Oct 6, 2013, at 10:13 PM, Matthew Rocklin <mrock...@gmail.com> wrote: >> >> This fails in solve >> >> In [1]: from sympy.stats import * >> >> In [2]: mu = Symbol('mu', real=True, bounded=True) >> >> In [3]: sigma = Symbol('sigma', positive=True) >> >> In [4]: X = Normal('X', mu, sigma) >> >> In [5]: simplify(2 * P(X - mu < 10)) >> Out[5]: >> ⎛ ___⎞ >> ⎜5⋅╲╱ 2 ⎟ >> erf⎜───────⎟ + 1 >> ⎝ σ ⎠ >> >> In [6]: solve(_ - 0.20, sigma) >> NotImplementedError: >> No algorithms are implemented to solve equation -_Dummy_44 + >> erf(5*sqrt(2)/sigma) >> >> Note that historically in statistics each distribution knew how to >> calculate these things on their own. It was hard coded in. In stats we >> express the problem with statistical operations and use SymPy to generate >> the right equations to solve in each case. This is usually far more >> powerful and extensible but, in this particular case, performs badly. The >> ideal path to solution here is to teach solve how to deal with error >> functions. >> >> Does anyone know how hard this is? >> >> >> Does the error function have an inverse? The variable only appears once in >> the expression, so as long as each function is invertible, solving such >> expressions is easy. >> >> Aaron Meurer >> >> >> On Sun, Oct 6, 2013 at 8:56 PM, Buck Shlegeris <buck.shlege...@anu.edu.au> >> wrote: >>> >>> I have the following code, using the statistics module. It answers >>> questions like "If there's a 20% chance that my random variable is within 10 >>> of the mean, what is the standard deviation?" with the call >>> getStdDev(10,20). >>> >>> def getStdDev(distance,confidence): >>> x = Normal(0,1) >>> confidenceDistance = x.confidence(confidence)[1] >>> stddev = confidenceDistance * distance >>> return stddev >>> >>> The statistics module lets me do this with the confidence method. >>> However, the statistics module is deprecated. >>> >>> Is there an equivalent in the stats module? >>> >>> -- >>> 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. >>> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> -- >> 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. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> -- >> 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. >> For more options, visit https://groups.google.com/groups/opt_out. > > > -- > 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. > For more options, visit https://groups.google.com/groups/opt_out. -- 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. For more options, visit https://groups.google.com/groups/opt_out.
