How long have you been using MATLAB? You have asked 51 questions on Answers. But just today, you asked two trivial questions in a row. You SERIOUSLY need to learn MATLAB. The gods of MATLAB gave us manuals for a reason. Spend some time doing the MATLAB Onramp tutorial. Or there are surely free tutorials to be found, perhaps look on YouTube.
If you want to form the sum, then use sum.
E = sum(E3d,3);
In this case, the sum operates on the third dimension of E3d.
