# Error using quiver The size of X must match the size of U or the number of columns of U.

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Cristobal Meza on 26 Apr 2022
Commented: Jan on 28 Apr 2022
k = 1
q = 2
x = 3
a = 4
y = 4
i = (k.*abs(q)).*(x+(a./2)) ./ (((x+(a./2)).^2)+y.^2)^(3./2) + (k.*abs(q)).*(x-(a./2)) / (((x-(a./2)).^2)+y.^2).^(3./2)
j = (k.*abs(q).*y) ./ (((x+(a./2)).^2)+y.^2).^(3./2) + (k.*abs(q).*y) / (((x-(a./2)).^2)+y.^2).^(3./2)
Er = sqrt((i.^2)+(j.^2))
E1_x = (k.*abs(q)).*(x+(a./2)) ./ (((x+(a./2)).^2)+y.^2).^(3./2)
E1_y = (k.*abs(q).*y) ./ (((x+(a./2)).^2)+y.^2).^(3./2)
E2_x = (k.*abs(q)).*(x-(a./2)) ./ (((x-(a./2)).^2)+y.^2).^(3./2)
E2_y = (k.*abs(q).*y) ./ (((x-(a./2)).^2)+y.^2).^(3./2)
Er_x = E1_x + E2_x;
Er_y = E1_y + E2_y;
Etot = sqrt( (Er_x.^2) + (Er_y.^2) )
[x,y] = meshgrid(-10:10,-10:10);
u = (Er_x)./Etot
v = (Er_y)./Etot
quiver(x,y,u,v)
Error using quiver The size of X must match the size of U or the number of columns of U.
Jan on 27 Apr 2022
@Cristobal Meza: I've formatted your code to improve the readibility. By the way, the overkill of parentheses reduced the clarity.

Jan on 27 Apr 2022
Edited: Jan on 27 Apr 2022
x = -10:10; % No need for meshgrid since Matlab R2016b
y = (-10:10).'; % simply use a row and a column vector
k = 1;
q = 2;
aq = abs(q); % Calculate it once only
a = 4;
% This is not used at all?! >>>>>>>>>
% i = k*abs(q) * ((x + a/2) ./ ((x + a/2).^2 + y.^2).^1.5 + ...
% (x - a/2) ./ ((x - a/2).^2 + y.^2).^1.5);
% j = k*abs(q) * (y ./ (((x+a/2).^2) + y.^2).^1.5 + ...
% y ./ (((x-a/2).^2) + y.^2).^1.5);
% Er = sqrt(i.^2 + j.^2);
% <<<<<<<<<<<
xp = ((x + a/2).^2 + y.^2).^1.5;
xm = ((x - a/2).^2 + y.^2).^1.5;
E1_x = k * aq * (x+a/2) ./ xp;
E1_y = k * aq * y ./ xp;
E2_x = k * aq * (x-a/2) ./ xm;
E2_y = k * aq * y ./ xm;
Er_x = E1_x + E2_x;
Er_y = E1_y + E2_y;
Etot = sqrt(Er_x.^2 + Er_y.^2);
u = Er_x ./ Etot;
v = Er_y ./ Etot;
quiver(x,y,u,v)
Instead of a fixed value for x and y, both coordinates are vectors of the coordinates here.
Do you see, that the code looks much cleaner? Then the symmetry of the formulas are obvious on first sight and typos would be prominent automatically. Keep the code simple.
##### 2 CommentsShowHide 1 older comment
Jan on 28 Apr 2022
You are welcome. It is the nature of teachers to tend to outdated information. :-)

R2022a

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