Find a root of a function in an interval.
Parameters :  f : function
a : number
b : number
xtol : number, optional
maxiter : number, optional
args : tuple, optional
full_output : bool, optional
disp : {True, bool} optional


Returns :  x0 : float
r : RootResults (present if full_output = True)

Notes
Uses [Ridders1979] method to find a zero of the function f between the arguments a and b. Ridders’ method is faster than bisection, but not generally as fast as the Brent rountines. [Ridders1979] provides the classic description and source of the algorithm. A description can also be found in any recent edition of Numerical Recipes.
The routine used here diverges slightly from standard presentations in order to be a bit more careful of tolerance.
References
[Ridders1979]  (1, 2, 3) Ridders, C. F. J. “A New Algorithm for Computing a Single Root of a Real Continuous Function.” IEEE Trans. Circuits Systems 26, 979980, 1979. 