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diff --git a/Measurements/At_f.m b/Measurements/At_f.m
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+% At_f.m
+%
+% Adjoint for "scrambled Fourier" measurements.
+%
+% Usage: x = At_f(b, N, OMEGA, P)
+%
+% b - K vector = [real part; imag part]
+%
+% N - length of output x
+%
+% 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 embedded.
+%     Default = 1:N (no scrambling).
+%
+% Written by: Justin Romberg, Caltech
+% Created: October 2005
+% Email: jrom@acm.caltech.edu
+%
+
+
+function x = At_f(b, N, OMEGA, P)
+
+if (nargin < 4),  P = 1:N;  end
+
+K = length(b);
+fx = zeros(N,1);
+fx(OMEGA) = sqrt(2)*b(1:K/2) + i*sqrt(2)*b(K/2+1:K);
+x = zeros(N,1);
+x(P) = sqrt(N)*real(ifft(fx));