[scilab-Users] RE: Concatenation with hypermatrix

[Mike Page]

Hi,

I think you have encountered a general problem with hypermatrices.  They are
quite fast to operate on when you work across some dimensions, but across
other dimensions they can be *VERY* slow.  I don't know why this is - maybe
somebody who wrote the hypermatrix code could look at it.

For instance, some time ago I had a need to extract a "slice" (that is a
matrix) from a hypermatrix.  This took a very long time, but when I
"transposed" the hypermatrix using the permute function, then it was much
faster.  I think if you arrange your dimensions so that the data to be
joined fits on the end of the existing storage then it will be faster.

Regards,
Mike.


-----Original Message-----
From: Orbeman [mailto:ludo.wag at laposte.net]
Sent: 01 June 2011 14:29
To: users at lists.scilab.org
Subject: [scilab-Users] RE: Concatenation with hypermatrix


I've finally found the command C=cat(3,C,x). It works but very slowly. For
exemple it needs more than 2 min to create a 890 * 2 * 5 3D hypermatrix, but
barely 1 sec to create the same data with 890 * (2+2+2+2+2) 2D matrix.

In fact, I've analysed n experiences which data (2 rows and variable line)
are written in one file per experience. All of the files are not the same
length, so I add number 'tag' to egal the maximun number of line, here 890.

After that I've created some others (hyper) matrix with different size of
row : 890 * 1 * 5, 890 * 3 * 5,...

I can imagine the increase of time for comptute.

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