rootSolve(func, xLow, xUpp, tol)

This function uses Ridder's Method to do non-linear root finding. This method works well for smooth scalar functions, and requires a bounded search space.
% XZERO = ROOTSOLVE(FUNC, XLOW, XUPP, TOL)
%
% FUNCTION: This function uses Ridder's Method to return a root, xZero,
% of func on the interval [xLow,xUpp]
%
% INPUTS:
% func = a function for a SISO function: y = f(x)
% xLow = the lower search bound
% xUpp = the upper search bound
% tol = return xZero if abs(func(xZero)) < tol
%
% OUTPUTS:
% xZero = the root of the function on the domain [xLow, xUpp]
%
% NOTES:
% 1) The function must be smooth
% 2) sign(f(xLow)) ~= sign(f(xUpp))
% 3) This function will return a root if one exists, and the function is
% not crazy. If there are multiple roots, it will return the first one
% that it finds.