What does a negative amplitude value in the Fourier domain mean?

Question

Say, i have a axis-symmertric square pulse, then take its Fourier transform (4th from last figure at http reference) i'd expect to see a sinc pulse. The fourier domain representation has a negative amplitude what does this mean, an an analogy would help? A phase change? an negative attenuation? Can the discrete FFT used by MATLAB represent these negative amplitudes, normally i plot the absolute of complex FFT values. thanks in advance.


http://dce.felk.cvut.cz/pjr/cviceni/ulohy/fft/index.htm

Answer 1

Negative values would be a phase of 180 degrees.