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Interpolate matrices for different times in Matlab

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mldmnn
mldmnn on 9 Aug 2018
Commented: 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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Accepted Answer

Stephen Cobeldick
Stephen Cobeldick on 10 Aug 2018
Edited: Stephen Cobeldick on 10 Aug 2018
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

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mldmnn
mldmnn on 10 Aug 2018
That is even better than the other answer! Nice to learn from experts!

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More Answers (1)

Ameer Hamza
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

mldmnn
mldmnn on 10 Aug 2018
It works very well. Thank you! Didn't think about using interp3 for this issue.

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