I have just written a program to calculate Legendre Polynomials, finding for Pl+1 using the recursion (l+1)Pl+1 + lPl-1 - (2l+1).x.Pl=0 That is working fine. The next section of the problem is to investigate the recursive polynomial in the reverse direction. I would solve this for Pl-1 in terms of Pl and Pl+1 - could someone please confirm if that is the correct way to 'reverse'? Also I would use the Rodriques formula to get the 2 starting values of Pn and Pn-1, it's a complex formula, is there a better way to get those starting values? Thanks for all help.