Unit:  SDL_fourier  Class:  TFastFourier  Declaration:  property FourSerCosCoeff[n: integer]:
double; 
The readonly array property FourSerCosCoeff
returns the coefficients A_{n} of the cosine terms of the Fourier series (cf. to equation below). The index n may assume values between 0 and SpectrumSize div 2. Accessing any value of the array below 0 and above SpectrumSize will result in a zero value on read, or in no action on write.
By using the above equation and the properties FourSerSinCoeff and FourSerCosCoeff the original curve can be reconstructed after a Fourier transform has been performed (of course, an inverse transform would do the
same).
Hint 1: 
In order to obtain "valid" results the property WeightingWindow has to be set to fwRectangle. 
Hint 2: 
Mind the subtle difference between the Magnitude and the Fourier series coefficients. The Magnitude does not preserve the signs, while the properties FourSerSinCoeff and FourSerCosCoeff do. 
Hint 3: 
FourSerCosCoeff could be easily calculated from RealSpec by adding the coefficients of
the corresponding negative and positive
frequencies. 
Hint 4: 
The index n into the property starts from zero (as opposed to the other array properties) 
