function[F,Xplot]= fftplot(x,M,deltat,pro)

% FFTPLOT calculates and plots a meaningful frequency domain
% representation of a signal.
%
% usage: FFTPLOT(x,M,deltat,proportion), x=input signal, M=M point FFT, deltat=sampling
% interval, proportion= ratio of fs to plot to. 
% if you want to plot 0 to fs/10, pro is equal to 10..

X=fft(x,M); X=deltat*X; % calculate the FFT
deltaf=deltat^-1/M; % determine the sampling frequency
upperbound=round(M/pro); % how far do we plot?

kplot=[0:upperbound+1]; % lets plot a little further
Xplot=X(1:upperbound+2); % matlab doesn't start counting at 0.

F=deltaf*kplot; % convert to Hz

plot(F,abs(Xplot)); xlabel('Frequency (Hz)'); grid; % plot.
axis([0 deltat^-1/pro 0 max(abs(X))+0.1*max(abs(X))]); %trim.