Date: Dec 3, 2012 11:18 PM
Subject: NaN with root finding method


I am using the 64 bit version of MatLab. I am trying to reproduce another groups work on a rootfinding method (which for sake of simplicity will say is llike an improved version of Steffensen's method).

My results agree with theirs for the first couple of iterations, but then when I get very close to the root, I get "NaN" for my output (and they don't: they give results for numbers as low as 10^(-600)).

I know using difference quotients and the like, when you're close to a root, you're basically dividing a number very close to zero by another number very close to zero, and so you can get numerical instabilities. I've applied the "double" command to every number I'm using and every computed value, but it doesn't solve my problem.
Any help or advice would be greatly appreciated.

Matt Brenneman