C# numerical recipes

Question

im begginer in C# and programming in general and i want to ask. I'm trying to make a project with datagridview in it and some calculations. Basicly what i want to do is from table of empirical data aproximate the data with chebyshev aproximation. Using code from numerical recipes i want to use this fuction, chebft and it looks like this:

void chebft(NRREAL a, NRREAL b, NRREAL c[], int n, NRREAL (*func)(NRREAL))
{ 
    int k,j;
    NRREAL fac,bpa,bma,*f;

    f=vector(0,n-1);
    bma=NR_1_2*(b-a);
    bpa=NR_1_2*(b+a);
    for (k=0;k<n;k++) {
    NRREAL y=cos(NR_PI*(k+NR_1_2)/n);
    f[k]=(*func)(y*bma+bpa);
    }
    fac=NR_2/n;
    for (j=0;j<n;j++) {
    NRZEAL sum=NR_0;
    for (k=0;k<n;k++)
        sum += f[k]*cos(NZ_PI*j*(k+NZ_1_2)/n);
    c[j]=fac*(NRREAL)sum;
    }
    free_vector(f,0,n-1);
}

and i want it to use in C# so what i have so far:

public void chebft(double a, double b, double[] c, int n, double func)  
    {
        int k,j;
        double fac, bpa, bma;

        double PI = 3.14159265358979323846;
        Vector f = new Vector(0, n - 1);
        bma = 0.5 * (b - a);
        bpa = 0.5 * (b - a);

        for (k = 0; k < n; k++)
        { 
            double y = Math.Cos(PI*(k+0.5)/n);
            f[k] = (func)(y*bma+bpa);
        }

        fac = 2.0 / n;
        for (j = 0; j < n; j++)
        {
            double sum = 0.0;

            for (k = 0; k < n; k++)
            {
                sum += f[k] * Math.Cos(PI * j * (k + 0.5) / n);
                c[j] = fac * (double)sum;
            }
        }

    }

I know there are mistakes in that func part and f[k] part, but i dont know how to fix them.

Thanks for help

Answer 1

The translation appears to be relatively solid with one exception (leaving aside possible numeric issues that require some more advanced knowledge of the problem to diagnose):

The function pointer func accepts a double-valued parameter and returns a double. To pass such a lambda function in C#, which is essentially equivalent to a function pointer in C++, use the following form:

Func<double, double> func

You can then call the function as follows:

f[k] = func(y*bma+bpa);

More information can be found here.

Also note that you do not need to cast sum to a double in the final loop, as it already is a double, and that the Math class already defines the constant Math.PI.