You can just do:
mean(x)
Ex = norm(x,2)^2 % the energy
Px = 1/numel(x)*norm(x,2)^2 % power
If you don't want to use norm(), you just use sum()
Ex = sum(abs(x).^2)
Px = 1/numel(x)*sum(abs(x).^2)
Note that the RMS of the signal is
sqrt(Px)
The Signal Processing Toolbox implements this as rms()
