How to save variable (Sum1) which is a plot , so that I can use it in later subsection to do some more computations.

 for ik=1:40
    Image = S(ik)*((abs(Phi(:,:,ik)).^2)); 
    Sum1= Sum1+Image;
 end   
    mesh(fftshift(X),fftshift(Y), fftshift(abs(Sum1)),'FaceColor','flat'); view(0,90);
    xlim([-2,2]); ylim([-2,2]);
    axis square;

[elham kreem]

i dont know what is the fuction s(ik) .

any way . because you have Sum1= Sum1+Image , in the loop , then you must put sum1=0 , before the loop .