How to understand the core code in FFT?

[Einsturing]

Hello! I can't understand the calculation method in FFT. o1_real = x.real * w1[0] - x.imag * w1[1] + b1[0] o1_imag = x.imag * w1[0] + x.real * w1[1] + b1[1] o2_real = o1_real * w2[0] - o1_imag * w2[1] + b2[0] o2_imag = o1_imag * w2[0] + o2_real * w2[1] + b2[1] Why should the real be '-', '+', '+', the imag be '+', '+', '+'? What role does this calculation combination play in it? Can I change the first '-' to '+' or vice versa? And what role does 'kept_modes' play in it? Dropout?

[swook]

Please refer to my answer to your original question, viewable at #8