Hello all, I want to build a class to describe a generating function (as used in the context of discrete probability distributions). It would have exactly the functionality of the Poly class, have a normalization constraint on the coefficients, have a few more special methods that I'd define, and be created with a different set of arguments. I want to be able to write
>>> gf = GeneratingFunction(10,4,4,2) # 0.5 + 0.2 x + 0.2 x^2 + 0.1 x^3 >>> print sum(gf.coeffs) # normalized coefficients 1.0 >>> print gf.expected_value() # a method i've written 0.9 >>> two_moment = gf * gf # usual arithmetic for Poly instances >>> print sum(two_moment.coeffs) 1.0 >>> print two_moment.expected_value() 1.8 My first thought was to subclass the Poly class, force the coefficients to be normalized, pass appropriate arguments to Poly.__init__, and write methods like GeneratingFunction.expected_value () for the added functionality I want. But there seems to be no Poly.__init__ method for me to override. If I override Poly.__new__ to accept the syntax I want to use (where the kth argument is the count of the kth item in the collection -- perfect for probability problems) then arithmetic for my generating functions breaks, as the __add__, __mul__, &c. methods call a "class method" which expect the arguments usually passed to Poly.__new__ and none other. Can I get the functionality I want by forcing GeneratingFunction.__new__ to perform all the same checks and magic on its argument that Poly.__new__ is already doing? Is there an easier way? Thanks for any help! Dhruv Bansal Center for Nonlinear Dynamics, UT Austin dh...@ph.utexas.edu http://dhruvbansal.com --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
