function y=fouriercompress(X,P);
 
 
 
% fouriercompress reconstructs an approximation of
% of a one-dimensional signal from P percent of its largest
% FFT coefficients
% X should be a 1xN row vector


X=double(X);                        % floating point
subplot(1,2,1);
plot(X);
axis([1 length(X) min(X) max(X)]);
title('original data');
M=length(X);
p=(100-P)/(100);
%

    
    tic                                 % start clock
    % start clock
	fX = fft(X);
     disp(['-----------']);
    disp('Forward FFT');
    toc                                 % stop clock
    disp(['-----------']);
    
    tic
	fcsort = sort(abs(fX(:)));          % sort fourier coeff by magnitudes     
    fcerr = cumsum(fcsort.^2);          % sum of squares
    fcerr = flipud(fcerr);              % decreasing order
	fthresh = fcsort(floor(p*M));       % specify threshold
	cf_X = fX .* (abs(fX) > fthresh);   % keep large
     disp(['-----------']);
    disp('Sorting/thresholding');
    toc
    disp(['-----------']);
    
    tic
	icf_X = ifft(cf_X);  
     disp(['-----------']);
    disp('Inverse FFT');
    toc
    disp(['-----------']);
    y=real(icf_X);
    subplot(1,2,2)
    plot(icf_X);
    axis([1 length(X) min(X) max(X)]);
	title('reconstruction from large Fourier coefficients');