% suppose we have 2 signal x and y
x= [1 0 0 2 0 2 0 0];
y= [1 1 0 0 0 2 0 0];
% then we transform the signals
Fx = fftn(x);
Fy = fftn(y);
% we get the real and image part form transformed
FxI= imag(Fx);
FxR= real(Fy);
FyI = imag(Fy);
FyR = real(Fy);
% the question is, where can we get the value of each component?
Each of FxI, FxR and others is an array. So, you can use it like FxI(1), or FxR(1:2) ...
the ouput of the fft is an array, equal to the size of the number of fft point you put in. So the first array element from the ouput of the fft function is the DC component e.g. Fxl(1), and the second array element is amplitude of the first frequency componet, that is, the first component unequal to the DC component, e.g. Fxl(2).
Pay attention; FxR= real(Fy) should be FxR= real(Fx).
In case it may help you, here is a custom matlab FFT code for real signals. It is meant to provide only the part of the spectrum needed (eg positive frequencies), accepts the time sampling for accurate frequency mapping, and corrects extremal amplitudes (dc and highest frequencies), so that "unit amplitude sines/cosines" peak at amplitude one in the frequency domain. An example is given. Corrections and suggestions welcome.
http://www.laurent-duval.eu/Documents-Common/FFTR.m
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