Using different colours in a quiver plot

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Karthik Nagarajan
Karthik Nagarajan on 6 Aug 2019
Commented: Adam Danz on 8 Aug 2019
Dear all,
I am creating a 2D quiver plot and I need to show some of the arrows in the figure in a different colour from the rest. To illustrate the issue, I will use the example given on quiver documentation page (https://www.mathworks.com/help/matlab/ref/quiver.html).
Suppose I plot a quiver plot with custom scaling as follows:
clear;clc;clf;
close all hidden;
[x,y] = meshgrid(0:0.2:2,0:0.2:2);
u = cos(x).*y;
v = sin(x).*y;
figure;
quiver(x,y,u,v,1.5)
Now let us say that I want all arrows for which the vector magnitude is greater than 1.0 to be shown in red. I have tried to add the following code:
hold on;
w=sqrt(u.^2+v.^2);
bk=find(w>1.0);
quiver(x(bk),y(bk),u(bk),v(bk),1.5,'color','r')
The result is as shown below:
quiver_test.jpg
Clearly, the second set of arrows have been scaled differently from the first set. I could work around this by manually adjusting the scale value in the second quiver command but this involves painstaking trial and error. May I know if there is a better solution?
Best,
Karthik.
  1 Comment
Karthik Nagarajan
Karthik Nagarajan on 6 Aug 2019
I should mention that I am using Matlab R2013A Student version.

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Answers (1)

infinity
infinity on 6 Aug 2019
Edited: infinity on 6 Aug 2019
Hello,
My suggestion is that you plot the first figure for the vectors that have magnitude less than 1.0 (using blue color) then you plot second figure for the rest of vectors (using red color).
  5 Comments
Adam Danz
Adam Danz on 8 Aug 2019
Instead of editing quiver.m, you should make a copy of that function, give it a unique name, and use that instead of quiver.m. Never manipulate a built-in matlab file.
When I open quiver.m using r2019a, try quiverparseargs() is called on line 41.
pvpairs = quiverparseargs(args);
catch ME
throw(ME)
end

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