I'm trying to evaluate a long expression with lots of summations and n choose k's. For some reason, the following expression (which is a part of the long expression) returns NaN. from sympy import * w_1_2_3 = symbols('w_1_2_3') w_1_3 = symbols('w_1_3') w_2_3 = symbols('w_2_3') w_1_2 = symbols('w_1_2') exprr = 7*Sum(binomial(5, w_1_2_3)*Sum(binomial(0, -w_1_2_3 + w_1_3)*binomial(2, w_1_2_3 - w_1_3 - 2)*binomial(13, 11 - w_1_2_3), (w_1_3, w_1_2_3, 5)), (w_1_2_3, 0, 5))/868017280 exprr.doit() -> NaN
However, if I evaluate each of the terms in the first sum separately, I get 0 for each of them (as should be): exprr2 = binomial(5, w_1_2_3)*Sum(binomial(0, -w_1_2_3 + w_1_3)*binomial(2, w_1_2_3 - w_1_3 - 2)*binomial(13, 11 - w_1_2_3), (w_1_3, w_1_2_3, 5)) for t in range(0, 6): res = exprr2.subs(w_1_2_3, t).doit() print(t, res) -> 0 0 1 0 2 0 3 0 4 0 5 0 What is going on here? Why do I get NaN for the overall term? I also posted a question in StackOveflow-https://stackoverflow.com/questions/73222278/sympy-doit-returns-nan-instead-of-zero -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/sympy/bd9abc43-562c-4ce1-8561-310e2b97dfdcn%40googlegroups.com.