First of all, you cannot use
Ex (with a capital
E) as a name for an expression, because
Ex is the name of the Cadabra expression object. Secondly, you cannot add pre-fix superscripts like this; the best you can do there is to use the
LaTeXForm property. So you can do
Now what do you wan to do next? This expression clearly only contains one term. Did you want to compute it for a particular metric and then determine the number of non-zero components?