Status: Accepted Owner: fabian.seoane Labels: Type-Defect Priority-Medium Milestone-Release0.6.4
New issue 1270 by fabian.seoane: documentation for RSolve http://code.google.com/p/sympy/issues/detail?id=1270 Put this mail from Mateusz into the docs: rsolve_X functions were meant as a low level interface for rsolve() which would use Mathematica's syntax. Anyway it's true that docstrings for rsolve_X aren't much helpful, so here is a brief guide. Given a recurrence relation: a_{k}(n) y(n+k) + a_{k-1}(n) y(n+k-1) + ... + a_{0}(n) y(n) = f(n) where k > 0 and a_{i}(n) are polynomials in n. To use rsolve_X we need to put all coefficients in to a list L of k+1 elements the following way: L = [ a_{0}(n), ..., a_{k-1}(n), a_{k}(n) ] where L[i], for i=0..k, maps to a_{i}(n) y(n+i) (y(n+i) is implicit). For example if we would like to compute m-th Bernoulli polynomial up to a constant (example was taken from rsolve_poly docstring), then we would use b(n+1) - b(n) == m*n**(m-1) recurrence, which has solution b(n) = B_m + C. Then L = [-1, 1] and f(n) = m*n**(m-1) and finally for m=4: >>> from sympy.core import Symbol >>> n = Symbol('n', integer=True) >>> rsolve_poly([-1, 1], 4*n**3, n) C0 + n**2 - 2*n**3 + n**4 >>> bernoulli(4, n) -1/30 + n**2 - 2*n**3 + n**4 For the sake of completeness, f(n) can be: [1] a polynomial -> rsolve_poly [2] a rational function -> rsolve_ratio [3] a hypegeometric function -> rsolve_hyper I hope now it's much clearer and I hope someone will consider writing rsolve() as an easy to fix task. It might be also beneficial to put this guide into rsolve_X docstrings. -- You received this message because you are listed in the owner or CC fields of this issue, or because you starred this issue. You may adjust your issue notification preferences at: http://code.google.com/hosting/settings --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy-issues" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sympy-issues?hl=en -~----------~----~----~----~------~----~------~--~---
