Problem in computing the curl of 2D velocity vector field

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

[Thorsten]

No, we don't know what's happening because you have not told us how you computed X, Y, UU and VV. Please do so and provide the code...

[Andreas Passos]

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

Answer 1

[Emanuele Spinosa]

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?

[Andreas Passos]

How did you sort the problem, I have the same issue. Can you explain please?

Answer 2

[Youssef Khmou]

Generally, the input velocity matrices may contain NaNs, try :

 sum(isnan(UU(:))); % must be zero if there is no NaN, same for VV

[Emanuele Spinosa]

yes, they're both 0, both for UU and VV... can it depend on X and Y matrices?