function xproberr(threshold, rangelow, rangehigh, p, pf, samples, seed) 
% xproberr(threshold, rangelow, rangehigh, p, pf, samples, seed)  Signal to  
%    noise ratio experiment for a Bernoulli signal with random noise.  The 
%    signal to noise ratio is swept over the given range, and the 
%    experimental and theoretical error probability are plotted against it. 
% 
%    threshold  threshold ratio for exeriment 
%    rangelow   low end of signal to noise range (in db) 
%    rangehigh  high end of signal to noise range (in db) 
%    p          probability of a positive on Bernoulli signal 
%    pf         probability function for noise:  must have mean of 0 
%    samples    number of experimental samples to use 
%    seed       seed for random number generator 
if rangelow>=rangehigh 
   error('invalid range') 
end 
if ispf(pf)==0 
   error('invalid probability function') 
end 
if inrange(mmean(pf), 0, 1e-4)==0 
   error('noise probability function must have mean 0') 
end 
v=var(pf); 
snr=[rangelow:3:rangehigh]; 
u=sqrt((10.^(snr./10)).*v); 
pfs=mfberni(p); 
ncf=getcf(pf); 
S=rvgen(getcf(pfs), 1, samples, seed); 
N=rvgen(ncf, 1, samples, rem(seed^2, 10000)); 
PE=zeros(size(snr)); 
PPE=(1-p)*(1-pval(ncf, threshold.*u))+p.*pval(ncf, (threshold-1).*u); 
for i=1:length(snr), 
   SN=S.*u(i)+N; 
   D=(SN>=threshold*u(i)); 
   PE(i)=(samples-sum(D==S))/samples; 
end 
subplot(1,1,1) 
snr2=(u.^2)./(v^2); 
loglog(snr2, PPE) 
hold on 
loglog(snr2, PE, 'r') 
hold off 
xlabel('Signal to Noise Ratio') 
ylabel('P(E), Prob of Error')