[sympy] Functional equations

2013-05-27 Thread F. B.
Generic Partial Differential Equations may yield arbitrary functions in their solutions. When matching this generic solutions to initial or boundary conditions, we get a functional equation: that is an equation whose variable is a function (without derivatives). If the function to be found has

Re: [sympy] Functional equations

2013-05-27 Thread Aaron Meurer
On Mon, May 27, 2013 at 12:14 PM, F. B. wrote: > Generic Partial Differential Equations may yield arbitrary functions in > their solutions. > > When matching this generic solutions to initial or boundary conditions, we > get a functional equation: that is an equation whose variable is a function >

Re: [sympy] Functional equations

2013-05-27 Thread F. B.
Wolfram Mathematica has RSolve: http://reference.wolfram.com/mathematica/ref/RSolve.html It is mainly used to solve recurrence equations, though it is able to accept functional equations too. Wikipedia on recurrence equations: http://en.wikipedia.org/wiki/Recurrence_relation On Monday, May 27

Re: [sympy] Functional equations

2013-05-27 Thread Aaron Meurer
SymPy also has rsolve(), but it only solves recurrence relations. Aaron Meurer On May 27, 2013, at 4:23 PM, "F. B." wrote: Wolfram Mathematica has RSolve: http://reference.wolfram.com/mathematica/ref/RSolve.html It is mainly used to solve recurrence equations, though it is able to accept funct

Re: [sympy] Functional equations

2013-05-28 Thread F. B.
If the functional equation contains f(a) and f(b), it can be reduced to a recurrence formula by k (x + 1) = a k x = b which is k = a - b x = b / (a - b) now the new function g(x) = f(k*x) displays the same equation as a recurrence equation [ g(x) = f(b), g(x+1) = f(a) ]. That was just an att

Re: [sympy] Functional equations

2013-05-28 Thread Aaron Meurer
I guess a recurrence relation is a special case of a functional equation. I didn't consider that a functional equation might be transformable to a recurrence relation via a change of variable. I'm not sure how well your way works. If you take the classical functional equation f(a + b) = f(a)*f(b