Interp3 Producing Unexpected Output?

Question

John Chilleri 2017-5-20

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/341082-interp3-producing-unexpected-output

评论： John Chilleri 2017-5-20

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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.

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Answer 1

Walter Roberson 2017-5-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/341082-interp3-producing-unexpected-output#answer_267762

在 MATLAB Online 中打开

>> 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.