Re: 3D matrix

[Francesco Potortì]

>    I am searching doc or site to learn about the 3D matrix manipulations. 

https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html
https://octave.org/doc/v4.0.1/Advanced-Indexing.html

>    How to multiply two 3D matrix. What rules are? Division? What happen
>when doing M3D.*N3D?....

Only element-by-element operations are defined on N-D arrays.  As
far as I understand, other operations (such a *) first convert the
tensor to a matrix.  However, somo built-in functions operate natively
on N-D arrays, for example fftn, ifftn, convn.

If you want to operate more generally on tensors, you may try this
package (I never did):

https://www.tensorlab.net/

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