using System;
using System.Collections.Generic;
using System.Text;

namespace CommonLib.math
{
  public  class airthm
    {
        //计算ω=exp（j*2*pi/n） 
        public static complex omega(int n)
        {
            complex x;
            x.a = Math.Cos(0 - 2 * Math.PI / n);
            x.b = Math.Sin(0 - 2 * Math.PI / n);
            return x;
        }
        public static complex[] dft(short[] signal, int n)  //(信号，计算结果的长度) 
        {
            int i, j;
            complex w1;
            w1 = omega(n);
            complex[] w = new complex[n];
            for (i = 0; i < n; i++)
            {
                w[i] = complex.powcc(w1, i);
            }
            complex[] f = new complex[n];
            complex temp;  //w[i]的次方 
            complex temp1; //f中单项的值 
            //耗时部分
            for (i = 0; i < n; i++)
            {
                f[i].a = 0;
                f[i].b = 0;
                for (j = 0; j < n; j++)
                {
                    temp = complex.powcc(w[i], j);
                    temp1 = complex.commul(signal[j], temp);
                    f[i] = complex.comsum(f[i], temp1);
                }
            }
            return f;
        }
        //求幅值  x  信号  n  信号长度  返回 幅值数组 
        public static double[] amplitude(complex[] x, int n)
        {
            int i;
            double temp;
            double[] amp = new double[n];
            for (i = 0; i < n; i++)
            {
                temp = x[i].a * x[i].a + x[i].b * x[i].b;
                amp[i] = Math.Sqrt(temp);
            }
            return amp;
        }
    } 
}