Apply function on layer of 3D Array

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Jonatan Menger
Jonatan Menger 2020-5-8
评论： Jonatan Menger 2020-5-19
Hello,
Assume I have the following 3D Array Hv:
v=reshape(rand(1,6),1,1,[]);
H=[1 0 0 0; 0 4 4 0; 0 4 4 0; 0 0 0 1];
Hv=bsxfun(@times,H,v);
I want to perform the operation expm() on each layer of Hv. So the output should be an array of the same dimension, with the expm(H) of every layer. I do not want to use a loop over the third dimension, and hope it is possible to perform the operation directly on the vector. I hope my question is understandable, I couldn't find a solution anywhere. Thanks alot.
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Stephen23
Stephen23 2020-5-11
"I do not want to use a loop over the third dimension"
A loop is likely to be the fastest and most efficient solution. Why do you wish to avoid a loop?
Jonatan Menger
Jonatan Menger 2020-5-19
Thanks for the answers. I was trying to improve the speed of my program which has three nested loops, with the inner one doing 12000 rounds each time. I thought, as matlab is optimized for working with arrays, that there is some way to do it more efficient. But maybe i'll just need to except the speed i've got now.

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回答（1 个）

Monika Phadnis
Monika Phadnis 2020-5-11
You can use 'arrayfun' function for your use case in the following way:
>> data_expm = arrayfun(@(i)expm(Hv(:,:,i)), 1:size(Hv,3), 'UniformOutput', false)
You can refer this answer for more information :
https://in.mathworks.com/matlabcentral/answers/504830-how-to-operate-on-2d-matrices-in-a-3d-array
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Rik
Rik 2020-5-11
As mentioned there, it is probably faster to use a loop instead of this.

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