sage: find_local_maximum( lambda u: up(omega=u) / abs(eMod(omega=u)), -1, 1)

Above, u takes some values in the given interval. Fix one of them. Then eMod(omega=u) is the value of eMod in this fixed u-value. One can apply the abs on it, getting a number. In contrast, in lambda u: up/abs(eMod) we have for each u as result a symbolic expression. And the abs is applied also symbolically.