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+% A_fhp.m
+%
+% Takes measurements in the upper half-plane of the 2D Fourier transform.
+%
+% Usage: b = A_fhp(x, OMEGA)
+%
+% x - N vector
+%
+% b - K vector = [mean; real part(OMEGA); imag part(OMEGA)]
+%
+% OMEGA - K/2-1 vector denoting which Fourier coefficients to use
+% (the real and imag parts of each freq are kept).
+%
+% Written by: Justin Romberg, Caltech
+% Created: October 2005
+% Email: jrom@acm.caltech.edu
+%
+
+function y = A_fhp(x, OMEGA)
+
+n = round(sqrt(length(x)));
+
+yc = 1/n*fft2(reshape(x,n,n));
+y = [yc(1,1); sqrt(2)*real(yc(OMEGA)); sqrt(2)*imag(yc(OMEGA))];
+