function pmf=mfgeo(p) 
% mfgeo(p)  generates a geometric pmf with parameter p 
if p<=0 | p>=1 
   error('invalid value for p') 
end 
X=round(log(1e-6/p)/log(1-p)+1.5); 
x=[1:X]; 
P=p*((1-p).^(x-1)); 
pmf=[1 1; x' P'];