Hi Abdallah,
To save memory only the number of x and y points are saved (size of field array) and the delta x and delta y are saved. From these values you can calculate the vectors x and y.
In the attached Matlab code I perform this operation and below is an excerpt of how you could program it.
xvector = linspace(-dx*0.5*size(Ef,2),dx*0.5*size(Ef,2), size(Ef,2));
yvector = linspace(-dy*0.5*size(Ef,1),dy*0.5*size(Ef,1), size(Ef,1));