Newton - Raphson method

Find the zero of a regular function with Newton - Raphsons' method.

It is a Matlab function that determines the zero of a regular real function.

zero=newton_raphson(function,error)

The function has two input variable: 'function' is a string that represents the function of which find the relative zero. It must be expressed with the real variable 'x'. 'error' is the tolerance for the algorithm's arrest.
The function returns the zero point of the real function. It plots, in a figure, the function and the tangents used for the search of the zero.