I looked under the mask at the discrete fourier simulink block under the SimPowerSystem and I don't quite understand what algorithm is used to get the magnitude and phase of a signal.

Suppose we are interested in the fundamental freq of 60hz (first harmonic):
-To get the real part, it multiplies the input signal by 2*sin(2*pi*60*t), and then takes  the mean.
-To get the imaginary part, it multiplies the input signal by 2*cos(2*pi*60t), and then takes the mean.
Then it converts the real and imag part to mag and phase.

I don't quite understand why it multiplies the signal by the sin and cos terms above to get the real and imag part. What algorithm is this? Can somebody explain?

Thanks