Why do I obtain Nan and Inf when trying to compute the curl of a vector field?

I want to calculate the vorticity of a flow field for a planar diffuser (simple geometry), then I do curl(x,y,u,v) but the curl that I obtain is Nan or Inf.

Even when I create a grid for a 0º ramp angle (basically a channel with rectangular grid) I obtain that. Grid spacing is not uniform in x-direction.

Thank you.

[Walter Roberson]

Posting code would help. http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

[Emilio L.]

The piece of code that does not work is only this curl function. As inputs I have a predefined grid and predefined velocities.

I only have "curl(x0,x1,u,v)" and when I use "curl(u,v)" it computes the curl right.

Then, the problem must be in the grid, but I cannot figure out what is wrong with my grid, as it is simply a rectangular one with non-uniform spacing.

Thank you for your answer.

[Walter Roberson]

Then attach your x0, x1, u, v values, possibly as a .mat .

[Emilio L.]

These are my values. Thanks again.

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/curl.html

"The arrays X and Y, which define the coordinates for U and V, must be monotonic, but do not need to be uniformly spaced. X and Y must have the same number of elements, as if produced by meshgrid."

The help information is more specific:

   The arrays X,Y define the
    coordinates for U,V and must be monotonic and 2D plaid (as if
    produced by MESHGRID).

However, if you examine x0, x1, they are what would be produced by ndgrid() instead of by meshgrid(). So you need

   c = curl(x0.',x1.',u0.',u1.');
   surf(x0.', x1.', c, 'edgecolor', 'none')

[Emilio L.]

Thank you so much, I solved my problem. I really appreciate your help.