function np=sample(pdf, rangelow, rangehigh, dx) 
% sample(pdf, rangelow, rangehigh, samples)  Helper function for convpf.   
%    Generates a row vector with the given sample spacing dx, sampled from 
%    the p values of pdf over the given range 
if ispf(pdf)==0 | isdiscrt(pdf)==1 
   error('invalid pdf') 
end 
if rangelow>rangehigh 
   error('invalid range') 
end 
x=xvals(pdf); 
TR=rangehigh-rangelow; 
R=max(x)-x(1); 
np=zeros(1, round(TR/dx-0.5)); 
p=pvals(pdf); 
X=rangelow; 
i=1; 
while X<=rangehigh, 
   if X<x(1) | X>max(x) 
      np(i)=0; 
   else 
      index=round(((X-x(1))/R)*length(x)); 
      if index==0 
         index=1; 
      end 
      np(i)=p(index); 
   end 
   X=X+dx; 
   i=i+1; 
end