Apply function on layer of 3D Array

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.

[Rik]

You will probably have to either use a loop, or replicate your data to use functions like cellfun to hide the loop. I don't really see a way around it.

[Stephen23]

"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]

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.

Answer 1

[Monika Phadnis]

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

[Rik]

As mentioned there, it is probably faster to use a loop instead of this.