# FOURIER is the jSpectral module of jLab.

``` FOURIER  Returns the Fourier frequencies for a given length time series.

F=FOURIER(M) returns the one-sided (or positive) Fourier frequencies
for a time series of length M.

F is a radian or angular frequency so that the Nyquist is at PI.

F=FOURIER(M,'two') instead returns the two-sided Fourier frequencies.
The default behavior is equivalent to F=FOURIER(M,'one').

F=FOURIER(DT,M) uses sample rate DT in calculating the frequencies, so
that the Nyquist will be at PI/DT.

Note that the highest resolved frequency, MAX(F), differs for even or
odd M.  For even M, it is the Nyquist PI/DT, but for odd M the Nyquist
is not resolved and the highest resolved frequency is (M-1)/M * PI/DT.

For the one-sided option, F has length FLOOR(M/2)+1, or M/2+1 for even
M, and (M+1)/2 for odd M.  For the two-sided option, F has length M.
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Array input

F=FOURIER(M) also works if M an array instead of a scalar.  In this
case, F is a cell array with LENGTH(M) elements.

F=FOURIER(DT,M) with M being an array works provided DT is either a
scalar or an array of the same length as M.
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