module contacts
    integer, parameter :: c_dbl = KIND(1d0)
    integer, parameter :: max_size = 3600;
    type :: contactside
        INTEGER  :: n   ! size of data in arrays
        REAL(c_dbl)  :: elasticity, poisson
        REAL(c_dbl)  :: radius(max_size), crown(max_size)
    end type

    contains
    !  FUNCTIONS/SUBROUTINES exported from dll:
    subroutine Hertz(load, side1, side2) BIND(C)
    implicit none
    !DEC$ ATTRIBUTES DLLEXPORT::Hertz
    ! Arguments
    REAL(8),value :: load
    TYPE(contactside) :: side1, side2

    ! Implementation omitted
    end subroutine Hertz

end module

public unsafe struct ContactSide
{
    const int MaxSize = 3600;
    int size;
    double elasticity, poisson;
    fixed double radius[MaxSize], crown[MaxSize];
    public ContactSide(double radius, double crown) : this(new double[] { radius }, crown) { }
    public ContactSide(double[] radius, double crown)
    {
        this.size=radius.Length;
        fixed (double* ptr1 = this.radius, ptr2 = this.crown)
        {
            for(int i = 0; i<size; i++)
            {
                ptr1[i]=radius[i];
                ptr2[i]=crown;
            }
        }
        this.elasticity=DefaultElasticity;
        this.poisson=DefaultPoisson;
    }

    public static double DefaultElasticity = 200000;
    public static double DefaultPoisson = 0.3;
}

class Program
{
    [DllImport("FortranContacts.dll", EntryPoint = "hertz", CallingConvention = CallingConvention.Cdecl)]
    public extern static void Hertz(double load, ref ContactSide side1, ref ContactSide side2);

    static void Main(string[] args)
    {
        ContactSide side1 = new ContactSide(8.0, 1200);
        ContactSide side2 = new ContactSide(new double[] { 22, 22.2, 22.8, 24.6, 25.8, 29.3 }, 10000);

        Hertz(1000, ref side1, ref side2);

    }
}

public struct ContactSide
{
    int size;
    double elasticity, poisson;
    double[] radius, crown;

    public ContactSide(double radius, double crown) : this(new double[] { radius }, crown) { }
    public ContactSide(double[] radius, double crown)
    {
        this.size=radius.Length;
        this.radius=new double[size];
        this.crown=new double[size];
        radius.CopyTo(this.radius, 0);
        this.crown= Enumerable.Repeat(crown, size).ToArray();
        this.elasticity=DefaultElasticity;
        this.poisson=DefaultPoisson;
    }

    public static double DefaultElasticity = 200000;
    public static double DefaultPoisson = 0.3;
}