/// <summary>
/// Calcul dune FFT sur un tableau de 1024 points Selon l'algorithme de Cooley–Tukey
/// </summary>
/// <param name="Y"> Y[] : array of 1024 (decimal) values on which FFT has to be performed </param>
/// <returns> Tc[] array of 1024 (complex) values of FFT </returns>
public static Complex[] FFT1024(decimal[] Y)
{
//calcul de la FFT surle tableau entrant Y[]
//resultant sortant dans le tableau Tc[]
int N = Y.Length;
if (N != 1024)
{
Console.WriteLine("nombre de points doit etre = 1024");
Console.WriteLine("FFT sera calculé sur 1024 points seulement avec FFT1024() ");
System.Environment.Exit(1);
}
Complex[] Tc = new Complex[1024]; // résultat de la FFT
Complex[] Ec = new Complex[512]; // Even (pair)
Complex[] Oc = new Complex[512]; // Od (impair)
decimal[] E = new decimal[512];
decimal[] O = new decimal[512];
double Re, Im;
for (int k = 0; k < 512; k++)
{
E[k] = Y[2 * k];
O[k] = Y[(2 * k) + 1];
}
Ec = DFT.DFTv2(E); // Ec ( Even - pair) DFT of Even indexed pat of signal
Oc = DFT.DFTv2(O); // Odd ( Odd - impair) DFT of Odd indexed pat of signal
for (int k = 0; k < 512; k++)
{
Complex temp = new Complex(0, 0);
Re = Math.Cos((double)-2 * Math.PI * ((double)k / (double)1024));
Im = Math.Sin((double)-2 * Math.PI * ((double)k / (double)1024));
temp = new Complex(Re, Im);
Oc[k] = Oc[k] * temp;
}
for (int k = 0; k < 512; k++)
{
Tc[k] = Ec[k] + Oc[k]; // Tc[k] = Ec[k] + exp(-2.i.pi.k/N).Oc[k]
Tc[k + (N / 2)] = Ec[k] - Oc[k]; // Tc[k+N/2] = Ec[k] - exp(-2.i.pi.k/N).Oc[k]
}
return(Tc);
}
/// <summary>
/// Calcul dune FFT sur un tableau de N points Selon l'algorithme de Cooley–Tukey
/// </summary>
/// <param name="Y"> y[] : array of (decimal) values on which FFT has to be performed </param>
/// <returns> Tc[] array of (complex) values of FFT </returns>
public static Complex[] FFTN(decimal[] Y)
{
//calcul de la FFT surle tableau entrant y[]
//resultant sortant dans le tableau Tc[]
int N = Y.Length;
Complex[] Tc = new Complex[N]; // résultat de la FFT
Complex[] Ec = new Complex[N / 2]; // Even (pair)
Complex[] Oc = new Complex[N / 2]; // Od (impair)
decimal[] E = new decimal[N / 2];
decimal[] O = new decimal[N / 2];
double Re, Im;
for (int k = 0; k < N / 2; k++)
{
E[k] = Y[2 * k];
O[k] = Y[(2 * k) + 1];
}
Ec = DFT.DFTv2(E); // Ec ( Even - pair) DFT of Even indexed pat of signal
Oc = DFT.DFTv2(O); // Odd ( Odd - impair) DFT of Odd indexed pat of signal
//Ec = FFT.FFTN(E); // Ec ( Even - pair) DFT of Even indexed pat of signal
//Oc = FFT.FFTN(O); // Odd ( Odd - impair) DFT of Odd indexed pat of signal
for (int k = 0; k < N / 2; k++)
{
Complex temp = new Complex(0, 0);
Re = Math.Cos((double)-2 * Math.PI * ((double)k / (double)N));
Im = Math.Sin((double)-2 * Math.PI * ((double)k / (double)N));
temp = new Complex(Re, Im);
Oc[k] = Oc[k] * temp;
}
for (int k = 0; k < N / 2; k++)
{
Tc[k] = Ec[k] + Oc[k]; // Tc[k] = Ec[k] + exp(-2.i.pi.k/N).Oc[k]
Tc[k + (N / 2)] = Ec[k] - Oc[k]; // Tc[k+N/2] = Ec[k] - exp(-2.i.pi.k/N).Oc[k]
}
return(Tc);
}