Maybe this bit from the docstring is causing confusion: When x is a polynomial f of a single variable y of order >= 1, rf(x,k) = f(y) * f(y+1) * ... * f(x+k-1) as described in Peter Paule, "Greatest Factorial Factorization and Symbolic Summation", Journal of Symbolic Computation, vol. 20, pp. 235-268, 1995.
So rf(x**3, 2) is x**3*(x + 1)**3. I'm not sure why this definition is made. It seems like a bad one, since there are two different ways to interpret rf(a, b) if a is a polynomial. It looks like this was changed in https://github.com/sympy/sympy/pull/8941. For the other two, I get the same thing as the docstring in SymPy 1.0 >>> rf(x, k).rewrite(binomial) binomial(k + x - 1, k)*factorial(k) >>> rf(n, k).rewrite(factorial) factorial(k + n - 1)/factorial(n - 1) These seem mathematically correct. It seems all three of these changed from SymPy 0.7.6 to SymPy 1.0. Aaron Meurer On Thu, Apr 28, 2016 at 5:28 PM, Peter Luschny <[email protected]> wrote: >> We still haven't updated SymPy Live to SymPy 1.0, so the output of >> some examples may be different. > > > Thanks! Maybe I expressed myself misleading. Also the output in my > yupyter notebook did not correspond to what is in the documentation. > > I have difficulty to understand the output of the three calls > below which are taken from the doc-pages I cited. > ----------------------------------------------------- > from sympy import rf, symbols, factorial, ff, binomial > from sympy.abc import x > n, k = symbols('n k', integer=True) > > rf(x**3, 2) # ? x**3*(x**3 + 1) > > rf(x, k).rewrite(binomial) # ? RisingFactorial(x, k) > > rf(n, k).rewrite(factorial) # ? RisingFactorial(n, k) > ----------------------------------------------------- > > Perhaps someone can enlighten me what to expect > and to tell me if the output of SymPy 1.0 is correct? > > Peter > > > -- > 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 [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/ad6fe0f9-d9b2-411a-ba3d-dc4b9378655a%40googlegroups.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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAKgW%3D6JbM%2BPyYz5fND%2BtUfX6%3D-kNW5Hf%2B5uoKFvd7Mv-K8gPcQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
