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diff --git a/Measurements/A_f.m b/Measurements/A_f.m
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+% A_f.m
+%
+% Takes "scrambled Fourier" measurements.
+%
+% Usage: b = A_f(x, OMEGA, P)
+%
+% x - N vector
+%
+% b - K vector = [real part; imag part]
+%
+% OMEGA - K/2 vector denoting which Fourier coefficients to use
+%         (the real and imag parts of each freq are kept).
+%
+% P - Permutation to apply to the input vector.  Fourier coeffs of
+%     x(P) are calculated.
+%     Default = 1:N (no scrambling).
+%
+% Written by: Justin Romberg, Caltech
+% Created: October 2005
+% Email: jrom@acm.caltech.edu
+%
+
+function b = A_f(x, OMEGA, P)
+
+N = length(x);
+if (nargin < 3), P = 1:N;  end
+
+fx = 1/sqrt(N)*fft(x(P));
+b = [sqrt(2)*real(fx(OMEGA)); sqrt(2)*imag(fx(OMEGA))];
+