Android Code Snippet Root of a function - Newton-Raphson algorithm

SubName: Newton
Author: Newton & Raphson

Description: Find root of a function

The attached algorithm finds a root of a single argument function (with limitations on the type of function).
It finds one root depending on the starting point which is an input to the algorithm.
The attached function sub is an example.

Sub Newton(x As Double) As Double
    Dim tolerance  As Double = .000000001 ' Stop If you're close enough
    Dim  max_count As Int = 200  ' Maximum number of iterations
    Dim dx As Double = 0.0001
    For count = 1 To max_count
        If Abs(function(x)) > tolerance  Then
            x = x - 2*dx*function(x)/ (function(x + dx) - function(x -dx))
        Else
            Return x
        End If
    Next  
    Log("Failed to find a zero")
    Return -999
End Sub

Sub function(x As Double) As Double
    Return Power(x,4)-5*x*x-x+1
End Sub

Tags: root, function, Newton