function d=mildiff(x,dt,dw,par)
%gives dx according to milstein scheme
%m=drift(x)
%s=sigma(x)
%s1 = sigma' (x)
m=par(1)+par(2)*x;
s= par(3)*x^par(4);
s1= par(3)*par(4)*x^(par(4)-1);
d=dt*m + dw*s + .5*s*s1*(dw^2 - dt);