using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using NagCFunctionsAPI;
 
namespace NAG_1D_Spline_Interpolant
{
    class Program
    {
 
 
        static void Main(string[] args)
        {
	        const int NE_NOERROR = 0;
	        int m = 14;
	        int ncap = 5;
	        int ncap7=ncap+7;
	        double [] lamdadata ={1.50, 2.60, 4.00, 8.00};
	        double [] x = {0.20, 0.47, 0.74, 1.09, 1.60, 1.90, 2.60, 3.10, 4.00, 5.15, 6.17, 8.00, 10.00, 12.00};
	        double [] y = {0.00, 2.00, 4.00, 6.00, 8.00, 8.62, 9.10, 8.90, 8.15, 7.00, 6.00, 4.54, 3.39, 2.56};
	        double [] w = {0.20, 0.20, 0.30, 0.70, 0.90, 1.00, 1.00, 1.00, 0.80, 0.50, 0.70, 1.00, 1.00, 1.00};
            double [] lamda = new double[ncap7];
            double [] c = new double[ncap7];

	        for (int i=4,j=0; i < ncap+3; i++,j++)
		    {
		        lamda[i]=lamdadata[j];
		    }
            
            Nag_Spline spline = new Nag_Spline();
            NagError fail = new NagError();
 
            spline.n = ncap7;
            spline.lamda = Marshal.AllocHGlobal(ncap7*sizeof(double));
            Marshal.Copy(lamda, 0, spline.lamda, ncap7);
            double ss = 0.0;
            double fit = 0.0;
            double xarg = 0.0;
 
            try
            {
                NagFunctions.e02bac(m, x, y, w, ref ss, ref spline, ref fail);
                switch (fail.code)
                {
                    case 248:
                        throw new Exception("The knots fail to satisfy the condition x[0] < lamda[4] <= lamda[5] <=...<= lamda[ncap7-5) < x[m-1]. Thus the knots are not in correct order or are not interior to the data interval.");
                    case 249:
                        throw new Exception("The weights are not all strictly positive.");
                    case 62:
                        throw new Exception("The values of x[r], for r = 0, 1, 2, ..., m - 1, are not in nondecreasing order.");
                    case 11:
                        throw new Exception("ncap7 < 8 (so the number of interior knots is negative) or ncap7 > mdist + 4, where mdist is the number of distinct x values in the data (so there cannot be a unique solution).");
                    case 250:
                        throw new Exception("The conditions specified by Schoenberg and Whitney (1953) fail to hold for at least one subset of the distinct data abscissae. That is, there is no subset of ncap7 - 4 strictly increasing values, x[R[0]-1],..., x[R[ncap7-5]-1], among the abscissae such that, x[R[0]-1] < lamda[0] < x[R[4]-1], x[R[1]-1] < lamda[1] < x[R[5]-1],...,x[R(ncap7-9]-1] < lamda[ncap7-9] < lamda[R[ncap7-5]-1]");
                    default:
                        break;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Marshal.Copy(spline.lamda, lamda, 0, ncap7);
            Marshal.Copy(spline.c, c, 0, ncap7);

	        Console.Write("\nNumber of distinct knots = {0}\n\n", ncap+1);
	        Console.Write("Distinct knots located at \n\n");
	        for (int j = 3; j < ncap+4; j++)
		        Console.Write("{0, 8:f4}{1}", lamda[j], (j-3)%6 == 5 || j == ncap+3?"\n":" ");
	            Console.Write("\n\n    J    B-spline coeff c\n\n");
		    for (int j = 0;  j < ncap+3; ++j)
		        Console.Write("    {0}  {1,13:f4}\n", j+1, c[j]);
                Console.Write("\nResidual sum of squares = ");
                Console.Write("{0, 11:e2}\n\n", ss);
                Console.Write("Cubic spline approximation and residuals\n");
                Console.Write("  r        Abscissa        Weight       Ordinate          Spline      Residual\n\n");
      
            for (int r = 0; r < m; ++r)
	        {
                /* nag_1d_spline_evaluate (e02bbc).
                 * Evaluation of fitted cubic spline, function only
                 */
                NagFunctions.e02bbc(x[r], ref fit, ref spline, ref fail);
                if (fail.code != NE_NOERROR)
                {
		            Console.Write(
                      "Error from nag_1d_spline_evaluate (e02bbc).\n{0}\n",
                      fail.char_array);
                }
	            else
	            {

                    Console.Write("{0, 3}    {1, 11:f4}    {2, 11:f4}    {3, 11:f4}     {4, 11:f4}    {5, 10:e1}\n",
			                r+1, x[r], w[r], y[r], fit, fit-y[r]);
                if (r < m-1)
                {
                    xarg = (x[r] + x[r+1]) * 0.5;
                    /* nag_1d_spline_evaluate (e02bbc), see above. */
                    NagFunctions.e02bbc(xarg, ref fit, ref spline, ref fail);
                    if (fail.code != NE_NOERROR)
                    {
                        Console.Write( "Error from nag_1d_spline_evaluate (e02bbc).\n%s\n",
                                        fail.char_array);
                    }
	                else
		            {
		                Console.Write("    {0,14:f4}             {1, 33:f4}\n", xarg, fit);
		            }
                }
            }
	      }
          Marshal.FreeHGlobal(spline.lamda);
        }
    }
}