Re: [ojAlgo-user] Populating matrices

[Nigel S. <nig...@gm...>]

Thanks Anders, works like a charm. We're back down to 0.3s.

Cheers
Nigel

2008/11/13 Anders Peterson <an...@op...>:
> On 13 nov 2008, at 11.32, Nigel Sim wrote:
>
>> Hi, I wonder if someone could please comment on the proper way to
>> populate blank matricies, with memory efficiency in mind.
>>
>> The example I have is loading a CSV file into the matrix. Previously I
>> used JAMA:
>> 1) Created the matrix (new Matrix(rowCount, colCount))
>> 2) Iterate over the rows:
>> 2.1)   Iterate over the columns
>> 2.1.1) Write to the array (currentMatrix.set(row, j,
>> Double.parseDouble(cols[remainingCols.get(j)]));)
>>
>> I adapted this to ojalgo, so now I use
>> 1) PrimitiveMatrix.FACTORY.buildZero(rowCount, colCount)
>> ....
>> 2.1.1) currentMatrix = currentMatrix.set(row, j,
>> Double.parseDouble(cols[colsOfInterest[j]]));
>>
>> This is very slow, in that the JAMA version takes 0.3 s to run, and
>> the ojalgo version takes 30+ seconds to run. Essentially because the
>> matrix set method seems to make a copy of the matrix, which it
>> returns. This does seem at odds with the java doc which indicates that
>> the physical stores are mutable, so I would assume the matrix should
>> also be mutable.
>
>
> Didn't know it was that slow... I rarely use the set-method in
> BasicMatrix, and when I do it's only to set a few (a small number) of
> elements.
>
> The BasicMatrix interface doesn't force implementations to be
> mutable, and the implementations BigMatrix, PrimitiveMatrix and
> ComplexMatrix are immutable. When you call set(...) nothing is
> copied, but a couple of new instances are created - a new BasicMatrix
> and a new MatrixStore - and they contain the old/previous MatrixStore.
>
> I'd do it like this:
>
> PrimitiveDenseStore.FACTORY.makeEmpty(rowCount, colCount);
>
> and then loop to set the elements the way you did before.
>
> You do not have to create a BasicMatrix instance, and if you worry
> very much about memory consumption then you probably shouldn't.
>
>
>> The other option appears to be to create a double array and copy it
>> into the matrix with the factory, but this will mean, for a short
>> time, there will be two copies of a potentially large array in memory.
>>
>> Any advice would be most helpful.
>
>
> Currently the only way to create a new BasicMatrix instance without
> using the set-method and without any "unnecessary" copying is to
> create a MatrixStore and then instantiate a BasicMatrix
> implementation by calling a constructor directly. The constructors in
> BigMatrix, PrimitiveMatrix and ComplexMatrix do not copy anything.
>
>
> /Anders
>
>
>
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