How to implement interpolation using Prelookup using a MATLAB function?

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Amr
Amr on 25 Nov 2025 at 8:24
Answered: Walter Roberson on 25 Nov 2025 at 20:48
I have data with size 1201 26 37 384
I want to interpolate the first three dimenssions to get the fourth F(dim1, dim2, dim3) = column with size 348.
I'm using interpolation Using Prelookup and Prelookup to interpolate the first three dimentions and get the output is the fourth diminsion.
How can I implement this using matlab function instead of the simulink blocks?
I have tried using `griddedInterpolant` inside MATLAB funciton, but seems Simulink does not like it.
Is there any ideas?

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Answers (2)

Chuguang Pan
Chuguang Pan on 25 Nov 2025 at 9:15
Ran in:
@Amr. interpn can be used for N-D interpolation (table lookup).
Data = rand(1201,26,37,384);
[X1,X2,X3] = ndgrid(linspace(0,2,1201),linspace(0,2,26),linspace(0,2,37));
[X1q,X2q,X3q] = ndgrid(linspace(1,2,50));
Data_query=arrayfun(@(idx) interpn(X1,X2,X3,Data(:,:,:,idx),X1q,X2q,X3q,'linear'),1:384,"UniformOutput",false);
Data_output = cat(4,Data_query{:});
size(Data_output)
ans = 1×4
50 50 50 384
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Walter Roberson
Walter Roberson on 25 Nov 2025 at 10:28
@Amr
I am confused about whether your target is implementation in Simulink (seems like it from your comments); or if your target is outside Simulink (as requested explicitly in your initial question) ?
Amr
Amr on 25 Nov 2025 at 11:00
Sorry for confusion.
I wanted to implement it in a Matlab function inside Simulink.
when I said that How can I implement this using matlab function instead of the simulink blocks? I meant to use the matlab function inside simulink instead of using Simulink interpolation Using Prelookup and Prelookup blocks.
I hope I have clarified it.

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Walter Roberson
Walter Roberson on 25 Nov 2025 at 20:48
Convert your 4D data into a 3D array together with an (1201*26*37) x 384 array. The 3D array values should be column indices into the N x 384 array, and "nearest" interpolation should be done (in order to ensure that the outputs are indeed column indices.)
So, interpolated F(dim1, dim2, dim3) will return column indices into the N x 384 array, and you then use the returned column indices to extract the appropriate 384 values.

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