using System;
using System.Runtime.InteropServices; /* Provides mappings between C# and native code */

namespace NumericalAlgorithmsGroup
{
  class Quadrature
    {
      static int kount;
      /* Delegate object, note that the scalar parameter is 'ref' */
      public delegate double  NAG_D01AJ_FUN (ref double output); 

      [DllImport("FLDLL214Z_nag.dll")] /* Import from DLL, the C# compiler provides a rudimentry check of the signature */
        public static extern void D01AJF(NAG_D01AJ_FUN fun, ref double a, ref double b,
                                         ref double epsabs, ref double epsrel, ref double result, ref double abserr, double [] w,
                                         ref int lw, int [] iw, ref int liw, ref int ifail);
      public static void Main()
        {
          double epsrel = 1.0e-4;
          double epsabs = 0.0;
          int lw = 2000;
          double [] w = new double[lw];
          int liw = lw/4;
          int [] iw = new int [liw];
          int ifail = 1;
          double abserr = 0.0;
          double result=0;
	  /* Create a delegate object */
          NAG_D01AJ_FUN FUNC = new NAG_D01AJ_FUN(func);
          double a = 0.0;
          double b = 2.0*Math.PI;
          D01AJF(FUNC, ref a, ref b, ref epsabs, ref epsrel, ref result,
                 ref abserr, w, ref lw, iw, ref liw, ref ifail);
          if (ifail != 0)
            {
              // throw exception
            }
          else
            {
              Console.WriteLine("Approximation to the integral = {0, 9:f5}", result);
              Console.WriteLine("Estimate of the absolute error = {0, 9:e2}", abserr);
              Console.WriteLine("Number of function evaluations ={0}", kount);
              Console.WriteLine("Number of subintervals used = {0}", iw[0]);
            }
        }
      public static double func(ref double x)
        {
          ++kount;
          double pi = Math.PI;
          double retval;
          retval =  (x*Math.Sin(x*30.0)/Math.Sqrt(1.0-x*x/(pi*pi*4.0)));
          return retval;
        }
    }
}