function f=relbw(s,g,mass,width)
%
global mpi
%
% This form for the energy dependent width follows Jackson, NC34(1964)1644
gamfact=(mass./sqrt(s)).*sqrt((s-4*mpi^2)./(mass^2-4*mpi^2)).^3;
gamma=width.*gamfact;
%
drho=s-mass^2+i*mass*gamma;
f=g./drho;