Plot the electric field distribution ?

how Plot the electric field distribution above the contour ?

 % Plot the electric field distribution
figure;
v_now;
[ex,ey]=gradient(v);
quiver(-ex,-ey);  %Quiver command creates a plot, E=-grad(V), hence the negative sign 
title('potential ')

how put contour in the same figure of electric field distribution?

Answer 1

[Mischa Kim]

Use hold all before or after the first plot command:

 quiver(...)   % replace the dots with your data
 hold all;
 contour(...)

[Mary Jon]

thanks Mischa Kim

 electric field distribution appear in the figure as dot not as Arrow or appear small Arrow ,what I must do to make this Arrow appear large

[Mischa Kim]

Mary, use the scale parameter:

 scale = 2;            % double length of vectors
 quiver(-ex,-ey,scale)

[Mary Jon]

 Thanks  Mischa

the figure appear exactly as I want it

[Mary Jon]

can I making these Arrows of electric field distribution as continuous lines instead of Arrows intersect the contour? How can do that?

Answer 2

[Antonio Cedillo Hernandez]

Here you have the full MATLAB code explained (in spanish but the first comment is the code): https://www.youtube.com/watch?v=k9srU6aQfL0