You can use an OutputFcn,
or simply add a line of code to your objective function to display x, or pause under certain conditions. You could also possibly set conditional or non-conditional breakpoints,
However, I feel I should mention that fminsearch uses the Nelder-Mead algorithm, which is not designed for problems with a large number unknowns. In theory, it is only guaranteed to converge for 1 unknown, and in practice its performance starts to degrade significantly beyond about 6 unknowns. In your case, with 100 unknowns, I am suprised you ever see good fminsearch behavior.
