How do you get FFT for negative $k$ values?

1. Can FFT have negative values?
2. What do negative values in FFT mean?
3. Can Fourier transform be negative?
4. Why are there negative frequencies in FFT?

Can FFT have negative values?

FFT gave a result in complex coordinates. Absolute value of all data points should be taken . Power values are absolute values of complex numbers derived from FFT. They can not be negative unless they are contrasted to baseline or other conditions.

What do negative values in FFT mean?

Negative values in the real component of the result of a complex FFT correspond to a negative correlation with a cosine waveform (same as a 180 degree phase shift). If you want to check the energy at each frequency, graph the magnitude (sqrt(rere+imim)) of each complex FFT result bin.

Can Fourier transform be negative?

The Fourier transform magnitude can be thought of as the length of the complex vector of X(e(j omega)) which is always a positive number.

Why are there negative frequencies in FFT?

The reason is that the Fourier transform is symmetric about the y-axis, because the Fourier transform is mathematically defined on the interval (-Inf,Inf). The actual Fourier transform therefore has negative frequencies.