I have a question about how to extract the time averaged magnitude of the poynting vector at a particular voxel from my simulations.

I ran a harmonic simulation of a dipole model, with an overall field sensor. When the simulation ended, I exported the S(x,y,z,f0) variable of the overall field sensor to matlab. Then, when I open the snapshot variable in matlab, I see three columns with numbers having a real and an imaginary part. I assume that each column corresponds to the x,y,z complex values of the poynting vector at each voxel. Then, my question is, in order to calculate the time averaged magnitude of the poynting vector at each voxel, should I just compute ½ times the real part of the complex values in this snapshot variable? Or should I compute the magnitude of these complex values by computing the square root of: real part squared + imaginary part squared?

Thanks.