function [a] = N(m,mp,w)
pp = size(w);
for i=1:pp(2)
 if ((w(i)==m)|(w(i)==mp)) 
  if (m==mp)
   a(i) = pi^2/4/m;
  else
   a(i) = 0;
  end;
 else
  w2 = w(i)*w(i);
  a(i) = mp*(sin(pi*w(i)).^2)/(w2-m*m)/(w2-mp*mp);
 end;
end;
% normalize it to a delta-function
a = a / (pi^2/4/m);
end;

