h=pheaviside(L);
pheaviside(L) returns a periodic Heaviside function. The periodic Heaviside function takes on the value 1 for indices corresponding to positive frequencies, 0 corresponding to negative frequencies and the value .5 for the zero and Nyquist frequencies.
To get a function that weights the negative frequencies by 1 and the positive by 0, use involute(pheaviside(L))
As an example, the pheaviside function can be use to calculate the Hilbert transform for a column vector f:
h=2*ifft(fft(f).*pheaviside(length(f)));