How to debug lineSearch, or fminusub?

Hi there,

I'm trying to run multiple solvers and their algorithms to solve for 2-6 parameters. This is working fine for almost all initial points, solvers and algorithms that I use. However, for some reason the fminunc solver runs into a NaN or Inf during some iteration with one specific inital point. The NaN/Inf occurs in the roots function, which is called by lineSearch, which is in turn called by fminusub, again called by fminunc. I would like to set a break point in the lineSearch function and find out what is happening here, however I can't seem to find the lineSearch function.

This is my error:

Error using roots (line 27)
Input to ROOTS must not contain NaN or Inf.

Error in lineSearch

Error in lineSearch

Error in lineSearch

Error in lineSearch

Error in fminusub (line 186)
          lineSearch(funfcn,x,dir,f,dirDerivative, ...

Error in fminunc (line 472)
   [x,FVAL,GRAD,HESSIAN,EXITFLAG,OUTPUT] = fminusub(funfcn,x, ...
       

Typing:

help lineSearch
% or
open lineSearch

returns:

Error using open (line 86)
File 'linesearch' not found.
% or
lineSearch not found.

lineSearch is called on line 186 in fminusub.m but it seems I can't open it. I can put break points inside root.m but all I see here is nondescript numbers and the offending Inf. I don't know at which point root is called with an Inf and why. Do you have any ideas on how to debug this?

Thank you.