# Numerical root finding using Secant Method in c#

By pete rainbow

## This class provides a simple method to find the roots of a formula, similar to the GOTO function in Excel

class Secant
{
public delegate double Function(double x);

/// <summary>
/// gets the root of the supplied formula, wthin a certain precision and iteration cutoff
/// pass in seed value
/// </summary>
/// <param name="prec">how precise an answer we want</param>
/// <param name="stepsCutoff">max steps</param>
/// <param name="changePoint">the starting point</param>
/// <param name="f">the formula</param>
/// <returns>the value of x if found, nan otherwise</returns>
public static double Execute( double prec , int stepsCutoff, double changePoint,  Function f )
{
double p2, p1, p0;
int i;
p0 = f(changePoint);
p1 = f(changePoint + 1);
p2 = p1 - f(p1) * (p1 - p0) / (f(p1) - f(p0));

for (i = 0; System.Math.Abs(p2-p1) > prec && i < stepsCutoff; i++)
{
p0 = p1;
p1 = p2;
p2 = p1 - f(p1) * (p1 - p0) / (f(p1) - f(p0));
}
if (i < stepsCutoff)
return p2;
else
{
System.Diagnostics.Debug.WriteLine("{0}.The method did not converge", p2);
return double.NaN;
}
}

public static void TestMe()
{
double res = Execute(.001, 20, 0, delegate(double x) { return x * x * x - 2 * x - 5; });
res = Execute(.001, 20, 0, delegate(double x) { return x * x  -4; });
}
}

Numerical root finding using Secant Method in c#  (2653 Views)