Приближенное вычисление интеграла от быстро осциллирующей функции

//---------------------------------------------------------------------------
 
#include <vcl.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
 
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
double *d, *x, *y, **Rec,**Imc, *ReD,*ImD;
double a,b,w,p,ref,imf,RedD,ImmD;
int n;
 
void findcoeff(void)
{
    p = w*(b-a)/2;
    for( int j = 0; j < n; j++)
    {
      int t = 0;
      double step = 0.25;
      for( double i = -1; i <= 1; i+=step)
      {
        double temp = 1;
        for( int k = 0; k < n; k++)
          if(j!=k)
            temp*=(i - d[k])/(d[j] - d[k]);
        Rec[j][t] = temp*cos(p*i);
        Imc[j][t] = temp*sin(p*i);
        t++;
      }
    }
}
 
void findDi(void)
{
  for(int j=0; j < n; j++)
  {
    for(int t = 1; t < n-1; t++)
    {
      ReD[j]+=Rec[j][t]*y[t];
      ImD[j]+=Imc[j][t]*y[t];
    }
    ReD[j] = 0.25*(ReD[j]+(Rec[j][n-1]*y[n-1] + Rec[j][0])*y[0]/2);
    ImD[j] = 0.25*(ImD[j]+(Imc[j][n-1]*y[n-1] + Imc[j][0])*y[0]/2);
  }
}
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
 
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  b = Edit2->Text.ToDouble();
  a = Edit1->Text.ToDouble();
  n = Edit3->Text.ToInt();
  w = Edit4->Text.ToDouble();
  Rec = new double *[n];
  Imc = new double *[n];
  for(int i = 0; i < n; i++)
  {
    Rec[i] = new double[n];
    Imc[i] = new double[n];
  }
  y = new double[n];
  ReD = new double[n];
  ImD = new double[n];
  for(int i = 0; i < n; i++)
    y[i] = StringGrid2->Cells[i][2].ToDouble();
  findcoeff();
  findDi();
  for(int i = 0; i < n; i++)
  {
    RedD += ReD[i];
    ImmD += ImD[i];
  }
  p = w*(b-a)/2;
  ref = (b-a)/2 * (cos(p)*RedD - sin(p)*ImmD);
  imf = (b-a)/2 * (cos(p)*ImmD + sin(p)*RedD);
  Label1->Caption = " I = " + FloatToStr(ref) + " + i(" + FloatToStr(imf) + ")";
  delete [] d;
  delete [] y;
  delete [] x;
  delete [] ReD;
  delete [] ImD;
  for(int i = 0; i<n; i++)
    delete [] Rec[i];
  delete [] Rec;
  for(int i = 0; i<n; i++)
    delete [] Imc[i];
  delete [] Imc;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Edit3KeyDown(TObject *Sender, WORD &Key,
      TShiftState Shift)
{
  if (Key == 13)
  {
    StringGrid2->Width = 160;
    StringGrid2->Visible = True;
    n = Edit3->Text.ToInt();
    if(n>=3)
      StringGrid2->Width = 66*n;
    StringGrid2->ColCount = n;
 
  }
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button2Click(TObject *Sender)
{
  b = Edit2->Text.ToDouble();
  a = Edit1->Text.ToDouble();
  n = Edit3->Text.ToInt();
  d = new double[n];
  x = new double[n];
  for(int i = 0; i < n; i++)
  {
    d[i] = StringGrid2->Cells[i][0].ToDouble();
    x[i] = (b+a)/2 + (b-a)*d[i]/2;
    StringGrid2->Cells[i][1] = FloatToStr(x[i]);;
  }
}
//---------------------------------------------------------------------------