function P=perm(n,m) 
% perm(n,m)  m permutations of n 
echo
if min(n)<0 
   error('undefined for n < 0') 
end 
if min(m)<0 
   error('undefined for m < 0') 
end 
if max(m>n)==1 
   error('undefined for m > n') 
end 
P = ones(size(m));
for j = 1:size(m)
   for i = 0:(m(j)-1)
      P(j) = P(j) * (n - i);
   end
end