# Problem in computing the curl of 2D velocity vector field

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Hi everyone,
I'm trying the compute the curl of a 2D velocity vector field using the function
[curlz,cav] = curl(X,Y,UU,VV);
X, Y are generated using meshgrid. However I obtain a matrix of NaNs and + - Inf ... Do you know what's happening? I think I followed the correct instructions from the Matlab Help... Please let me know.
Emanuele
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Andreas Passos 2021-2-25

Hi, I want to calculate the curl from a single trajectory.
Basically, I want to identify if the trajectory rotates clockwise of anti-clock wise and measure the rotation speed.
I use something like the below:
x = data(:,1);
y = data(:,2);
u = data(:,3);
v = data(:,4);
V = [u v];
R = [x y];
curlRes = curl(V,R);
The result is 0 everywhere.
I also tried [curlz,cav] = curl(x,y,u,v) and it gives the follwoing error
'Index in position 1 is invalid. Array indices must be positive integers or logical values.'
the vectors u,v contain negative values as well as they indicate the velocity direction
Thank you

### 采纳的回答

Emanuele Spinosa 2014-12-3
I sorted out the problem, however it seems that the curl is too big at the extremes of the domain... any idea how to fix this?
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Andreas Passos 2021-2-25
How did you sort the problem, I have the same issue. Can you explain please?

### 更多回答（1 个）

Youssef Khmou 2014-12-3
Generally, the input velocity matrices may contain NaNs, try :
sum(isnan(UU(:))); % must be zero if there is no NaN, same for VV
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Emanuele Spinosa 2014-12-3
yes, they're both 0, both for UU and VV... can it depend on X and Y matrices?

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