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Re: Instructions for Installing BLAS and LAPACK library on Octave 5.2.0

From: Ian McCallion
Subject: Re: Instructions for Installing BLAS and LAPACK library on Octave 5.2.0
Date: Mon, 28 Sep 2020 20:45:46 +0100

On Mon, 28 Sep 2020 at 19:34, Nicholas Jankowski <> wrote:
> On Mon, Sep 28, 2020 at 1:46 PM Ilaya Bharathi <> 
> wrote:
>> Is it an openblas library which enables the multithreading is inbuilt with 
>> octave ?
> I haven't done this myself, just reading the information and this thread from 
> Ian that seems to be the case.
>> If so, please clarify which dll file(librefblas.dll or libopenblas.dll ) 
>> needs to be pasted where. If this is not the case, let me know what to do 
>> for the multithreading to work.
> based on the file names, I would assume the librefblas.dll is the  NetLib 
> reference BLAS and  libopenblas.dll is the OpenBLAS that Ian mentioned.

That's right, but the default is openblas, so you won't have to do any
dll copying. openblas is much faster than the reference blas.
>> finally, after implementing the multithreading feature. how to check it 
>> whether it's implemented or not ?
> again, I would try something like what Ian mentioned:
> >This means if you have a program such as:
> >   a = rand(1, 1000000);
> >   b = a*a;

Yes, except of course it should be

And you should probably set
a= rand(1,100000000);
to see any significant CPU time.

> >then Octave will automatically use openBLAS to do the calculations. By 
> >default openblas uses all processor threads. You can configure the number of 
> >threads using the environment >variable OPENBLAS_NUM_THREADS.

Cheers... Ian

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