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mldmnn
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Interpolate matrices for different times in Matlab

Asked by mldmnn
on 9 Aug 2018
Latest activity Commented on by mldmnn
on 10 Aug 2018
I have computed variables stored in a matrix for a specific time vector. Now I want to interpolate between those whole matrices for a new time vector to get the matrices for the desired new time vector.
I've came up with the following solution but it seems clunky and computational demanding:
clear all;
a(:,:,1) = [1 1 1;2 2 2;3 3 3]; % Matrix 1
a(:,:,2) = [4 4 4;6 6 6;8 8 8]; % Matrix 2
t1 = [1 2]; % Old time vector
t2 = [1 1.5 2]; % New time vector
% Interpolation for each matrix element
for r = 1:1:size(a,2)
for c = 1:1:size(a,1)
tab(:) = a(r,c,:);
tabInterp(r,c,:) = interp1(t1,tab(:),t2);
end
end
The result is and should be:
[2.5000 2.5000 2.5000
4.0000 4.0000 4.0000
5.5000 5.5000 5.5000]
Any thoughts?

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2 Answers

Answer by Stephen Cobeldick on 10 Aug 2018
Edited by Stephen Cobeldick on 10 Aug 2018
 Accepted Answer

Simpler in just one line and more efficient without all of those intermediate variables:
>> a(:,:,1) = [1 1 1;2 2 2;3 3 3];
>> a(:,:,2) = [4 4 4;6 6 6;8 8 8];
>> b = permute(interp1([1,2],permute(a,[3,2,1]),[1,1.5,2]),[3,2,1])
b(:,:,1) =
1 1 1
2 2 2
3 3 3
b(:,:,2) =
2.5000 2.5000 2.5000
4.0000 4.0000 4.0000
5.5000 5.5000 5.5000
b(:,:,3) =
4 4 4
6 6 6
8 8 8
And compared to your original code:
>> isequal(tabInterp,b)
ans = 1

  1 Comment

That is even better than the other answer! Nice to learn from experts!

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Answer by Ameer Hamza
on 9 Aug 2018

You can use interp3 as follow:
clear all;
a(:,:,1) = [1 1 1;2 2 2;3 3 3]; % Matrix 1
a(:,:,2) = [4 4 4;6 6 6;8 8 8]; % Matrix 2
t1 = [1 2]; % Old time vector
t2 = [1 1.5 2]; % New time vector
% Interpolation for each matrix element
[X, Y, Z] = meshgrid(1:size(a,1), 1:size(a,2), t1);
[X2, Y2, Z2] = meshgrid(1:size(a,1), 1:size(a,2), t2);
tabInterp = interp3(X,Y,Z,a,X2,Y2,Z2);

  2 Comments

It works very well. Thank you! Didn't think about using interp3 for this issue.

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