xmax=10e-2;
dx=xmax/10;

[X,Y]=meshgrid(0:dx:xmax,0:dx:xmax)

V=400.*(X.^2).*Y
%V=200*sin(X).*cos(Y)

contourf(X,Y,V)
%surf(X,Y,V)

[Ex,Ey]=gradient(-V,dx,dx)
Eabs=sqrt(Ex.^2+Ey.^2)
figure, surf(X,Y,Eabs)