Interp3 Producing Unexpected Output?

3 views (last 30 days)
Hello,
When using the default trilinear interpolation of interp3, I'm getting an unexpected output:
>> Interpval = interp3(X,X,X,V,X(10),X(5),X(1))
Interpval =
2.373878950731685e+04
>> V(10,5,1)
ans =
2.423129551369272e+04
where X is an n x 1 vector, and V is an n x n x n matrix.
I expected the two results to match as it should notice that the interpolation point is a grid point.
Why do the results not match?
Hopefully I'm just tired and this is a trivial question.
Thanks for your time and help.

Accepted Answer

Walter Roberson
Walter Roberson on 20 May 2017
>> X = sort(randn(1,25));
>> V = rand(25,25,25);
>> Interpval = interp3(X,X,X,V,X(10),X(5),X(1))
Interpval =
0.505428142457703
>> V(10,5,1)
ans =
0.844855674576263
>> V(5,10,1)
ans =
0.505428142457703
In other words, confusion over the fact that interp3's first coordinate is X, second coordinate is Y, whereas indexing in MATLAB has first coordinate corresponding to Y and second coordinate corresponding to X.
  1 Comment
John Chilleri
John Chilleri on 20 May 2017
This was the case - I wasn't thinking about grids, I was thinking about 3D space. Row and column formatting switch the X and Y...
Thank you!

Sign in to comment.

More Answers (0)

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by