On Mar 10, 7:32 pm, Nathan Pinno <[EMAIL PROTECTED]> wrote: > Thanks on the factoring bit, but I did mean factorial, not factoring. > How do I code that correctly, so that I can figure the following > equation out: cos(Pi * (z-1)! / z).
Is z an integer in this expression? (Note: it's not an equation--- there's no equality sign.) This looks suspiciously like a formula that's supposed to be valid for real and possibly even complex z, in which case what you're after is the gamma function. (gamma(z) = (z-1)!). The real version of this should certainly be present in numpy/scipy, and possibly the complex version too. If z really is supposed to be an integer then you should be aware that evaluating the expression directly is going to give almost no accuracy, for z greater than 30 or so: the absolute error in the argument to cosine will likely be much larger than 2*pi, so that the result of the cos() evaluation is meaningless. You might be better off computing w = (factorial(z-1) % (2*z)) as an integer; then cos(pi*(z-1)!/z) can be computed as cos(pi * w/z). Also, there are algebraic simplifications possible. If z is an integer greater than 4, and not a prime number, then the value of your expression is always going to be 1. If z is a prime number then Wilson's theorem is going to come in handy. (Google "Wilson's theorem prime"). Where does the expression come from? Is z a real or an integer? Is this a genuine real-world formula, or something that appeared in an elementary number theory textbook? Mark -- http://mail.python.org/mailman/listinfo/python-list
