[Octave-bug-tracker] [bug #59840] repmat and repelem slower than needed, faster implimentation suggested

[anonymous]

Follow-up Comment #8, bug #59840 (project octave):

After letting it run all night and generating over a gigabyte of timing for
every combination data I found a simple function for where to switch between
the kron and idx implementations for both repmat and repelem:

if m*n*p*q<128e3 and double precision, kron normally faster otherwise idx
faster

if m*n*p*q<128e3*2 and single precision, kron normally faster otherwise idx
faster

There is a significant increase in computation time at the above switch
location for both methods.

As having the precision doubled the product constant I'm confident the
difference in speed is related to memory. This may mean the constant is
different for different computers.

I have attached the code and some small data files. I have drawn a line for
the transition between the methods below the timing plots, currently it is for
single precision (remove the times 2 for double precision).

(file #50748)
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Additional Item Attachment:

File name: repmatrepelemfaster.m          Size:20 KB
    <https://file.savannah.gnu.org/file/repmatrepelemfaster.m?file_id=50748>



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