Why am I getting NaN using interp2?

• I have a 450*90 matrix of values
• I want to sample the matrix at 100 random sample points

However, while my interp2 function runs without errors, my output results vector contains NaN values after the 90th index.

The code below results in me getting NaN for points after the 90th index of vals - why, and how do I correct it?

Shouldn't I be able to sample 1 point from the matrix, or 50, or 100, or 1000 points?

Code:

row_vect = 1:450;
col_vect = 1:90;
[X,Y] = meshgrid(col_vect, row_vect);
V = abs(rand(450,90));
Xq = row_vect(1:100);
Yq = randi(89, 1,100);
vals = interp2(X, Y, V, Xq', Yq');

Thanks

Answer 1

[Torsten]

You try to extrapolate in Y-direction.

Read the description part for interp2 under

http://de.mathworks.com/help/matlab/ref/interp2.html

and you'll see why you get NaN for Y-values greater 90.

Best wishes

Torsten.

[macdommy74]

Thanks Torsten ....your answer is exactly correct for my question .... however, I made a mistake in my question.

I will edit my original question.

All Y values should be within 1-90.

[Torsten]

Use

[X,Y] = meshgrid(row_vect, col_vect);

instead of

[X,Y] = meshgrid(col_vect, row_vect);

Best wishes

Torsten.

[macdommy74]

I think this worked - thanks a million!!

Answer 2

[Walter Roberson]

Your problem is your X not your Y. max(X(:)) is 90 because your first argument to meshgrid() is col_vec which is 1:90

[macdommy74]

I think this worked - thanks a million!!