/// <summary>
/// Forward short-time Fourier Transform.
/// </summary>
/// <param name="A">Array</param>
/// <returns>Array</returns>
public Complex32[] Forward(Complex32[] A)
{
// params
int N = A.Length, i, j;
Complex32[] B = new Complex32[N];
int frame = coefs.Length;
// Short-Time Fourier Transform
for (i = 0; i < N; i += frame)
{
Complex32[] data = new Complex32[frame];
for (j = 0; j < frame; j++)
{
data[j] = A[i + j] * coefs[Maths.Mod(i - frame / 2, frame)];
}
data = FFT.Forward(data);
for (j = 0; j < frame; j++)
{
B[i + j] = data[j];
}
}
return(B);
}
/// <summary>
/// Forward Zak transform.
/// </summary>
/// <param name="A">Array</param>
/// <returns>Array</returns>
public float[] Forward(float[] A)
{
// Fast shaping orthogonalization algorithm
// WH functions using a discrete Zak transform.
// V.P. Volchkov, D.A. Petrov and V.M. Asiryan.
// http://www.conf.mirea.ru/CD2017/pdf/p4/66.pdf
int N = A.Length;
float[] vort = new float[N];
int L = N / M, L2 = L * 2, i, j;
Complex32[,] G = new Complex32[L2, N];
Complex32[,] Z;
for (i = 0; i < L2; i++)
{
for (j = 0; j < N; j++)
{
G[i, j] = A[Maths.Mod(j + M / 2 * i, N)];
}
}
if (Maths.IsPower(L2, 2))
{
Z = FFT.Forward(G);
}
else
{
Z = DFT.Forward(G);
}
float w = 2 / (float)Math.Sqrt(M);
float even, odd, phi;
Complex32 z1, z2;
for (i = 0; i < L; i++)
{
for (j = 0; j < N; j++)
{
z1 = Z[i, j];
z2 = Z[L + i, j];
even = (float)Math.Pow(z1.Abs, 2);
odd = (float)Math.Pow(z2.Abs, 2);
phi = w / (float)Math.Sqrt(even + odd);
Z[i, j] = z1 * phi;
Z[L + i, j] = z2 * phi;
}
}
Complex32 sum;
for (i = 0; i < N; i++)
{
sum = 0;
for (j = 0; j < L2; j++)
{
sum += Z[j, i];
}
vort[i] = (sum / L2).Real;
}
return(vort);
}
