Quiver lines on contour not showing

Hi there, I have a contour plot which I successfully generated. However when I turn on the quiver lines, they do not show up on the plot. Below is my code:

 [x,y] = meshgrid([1:0.1:6],[1:0.1:6]); %Creates axis.

 f  = 8.9875517873681764*10^9;
 PC1 = 1e-6;     %Charge of point one.
 PC2 = 1e-6;     %Charge of point two.
 PC3 = 0.5e-6;   %Charge of point three.
 n = 20;         %N-number of levels.

 %Charge of individual points.
 Charge1 = (f.*PC1)./sqrt((x-3).^2+(y-3).^2);
 Charge2 = (f.*PC2)./sqrt((x-5).^2+(y-3).^2);
 Charge3 = (f.*PC3)./sqrt((x-4).^2+(y-4).^2);

 Sum = Charge1-Charge2+Charge3;

 figure(1)

 [px,py]=gradient(Sum);

 contour(x,y,Sum,n)
 hold on
 quiver(x,y,px,py)
 hold off

Does anyone have an idea why the quiver lines are not showing? Thanks.

Answer 1

[Star Strider]

There seems to be a problem with the way you’re calculating the gradient. Making these changes will allow you to see the vectors and the contour plot (that I temporarily turned into contourf to make it visible). I will defer to you to determine what you need to do to fix it with the vector scaling turned back on:

   [px,py]=gradient(Sum, 1E+4, 1E+4);         % Set Derivative Intervals

   figure(1)
   contourf(x,y,Sum,n)
   hold on
   quiver(x,y,px,py,0)                        % Turn Off Scaling
   hold off

[Armando Marchena]

Thanks you very much.

[Star Strider]

My pleasure.