Arrow lengths don't represent the ratio of velocities for 2 Quiver Plots

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PASUNURU SAI VINEETH 2023-5-27

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评论： PASUNURU SAI VINEETH 2023-5-28

I have plotted two sets of velocity data for the same position data in a single quiver plot.

figure
quiver(xposition,yposition,uvelocity,vvelocity,'b')
hold on
quiver(xposition,yposition,v2dprime(1,:)',v2dprime(2,:)','r')
axis equal

But, visually from Figure 1, the length of arrows of the second dataset (red) is huge in comparison to the first dataset (blue). This is happening despite the actual velocities being comparable or in some cases, uvelocity(vvelocity) being greater than v2dprime. I would like the length of vectors originating at every point to represent the actual ratio of velocities. If I turn the scaling off, the first dataset (blue) is weirdly magnified as in Figure 2.

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Answer 1

VBBV 2023-5-27

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在 MATLAB Online 中打开

Data.mat

D = load('Data.mat');

figure

quiver(D.xposition,D.yposition,D.uvelocity,D.vvelocity,'b','AutoScaleFactor',2.5)

hold on

quiver(D.xposition,D.yposition,D.v2dprime(1,:)',D.v2dprime(3,:)','r')

% axis equal

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VBBV 2023-5-27

If you use AutoScaleFactor, property you can set the arrow lengths according to red color graph,

PASUNURU SAI VINEETH 2023-5-28

Thanks for the response. An AutoScaleFactor of 30 for blue graph is keeping things in proportion. Is it always trial and error though? I was hoping there would be a way the program can take care of it.

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Answer 2

鑫源 2023-5-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1974514-arrow-lengths-don-t-represent-the-ratio-of-velocities-for-2-quiver-plots#answer_1245874

在 MATLAB Online 中打开

plot the histogram, you 'll find the blue one in fact exists a few exaggeratedly large vecs. Though average length of the blue one and the red are comparalbe. I think that's the problem

C={[uvelocity, vvelocity],[v2dprime(1,:)',v2dprime(2,:)'],}
D=cellfun(@(x)vecnorm(x,2,2),C,UniformOutput=false);
>> histogram(D{1})
>> histogram(D{2})