public FFTWTransform(int size)
{
Size = size;
_dataOut = new double[Size / 2];
DataInPtr = FFTW.fftw_alloc_real(Size);
DataOutPtr = FFTW.fftw_alloc_complex(Size);
Plan = FFTW.fftw_plan_dft_r2c(1, ref size, DataInPtr, DataOutPtr, 0);
_window = Enumerable.Range(0, Size).Select(n => WindowFunction(n, Size)).ToArray();
_windowFactor = 1 / Math.Pow(_window.Average(), 2);
}
private bool disposedValue = false; // To detect redundant calls
protected virtual void Dispose(bool disposing)
{
if (!disposedValue)
{
if (disposing)
{
// managed
}
// unamanaged
FFTW.fftw_free(Plan);
disposedValue = true;
}
}
public double[] Transform()
{
FFTW.fftw_execute(Plan);
unsafe {
var pOut = (double *)DataOutPtr;
for (var i = 0; i < _dataOut.Length; i++)
{
var real = *(pOut + 0);
var imag = *(pOut + 1);
_dataOut[i] = Math.Sqrt(real * real + imag * imag);
pOut += 2;
}
}
// https://www.wavemetrics.com/products/igorpro/dataanalysis/signalprocessing/powerspectra.htm
Core.Multiply_IV64fS64f_IV64f(_dataOut, 0, 1 * _windowFactor / (double)Size, _dataOut.Length);
return(_dataOut);
}