Mark,
I now see (more fully) what you mean about the extra copy operations and agree that
there is a little more to do than what I responded below. Using getElement and
getDataRef for the current instance should suffice, however, in most cases. I need to
understand better what you are proposing.
Phil
-----Original Message-----
From: Phil Steitz
Sent: Mon 10/11/2004 10:16 AM
To: Jakarta Commons Developers List
Cc:
Subject: Re: cvs commit:
jakarta-commons/math/src/test/org/apache/commons/math/linear RealMatrixImplTest.java
Mark R. Diggory wrote:
> Hey Phil,
>
> Thanks for working on the RealMatrixImpl, it really gets things rolling.
> I was working on some things offline to support it further. One point of
> concern I have is that I thought we were going to make RealMatrixImpl
> "immutable" and allow the submatrix accessors return implementations
> that reference the internal matrix structure.
Yes, I was planning to remove the setters next.
>
> So, currently I would recommend our using an implementation of
> RealMatrix that maintains a reference to the original data[][] array and
> the submatix dimensions it is working within on that matrix. I have been
> working on such an implementation upto this point. Your adding the
> methods to the interface is good and I'll start working on
> implementations that use this strategy.
What do you mean here? I agree with J that getDataRef should be supported
only in the RealMatrixImpl (where I would leave it in)
>
> I also notice in the implementations there a great degree of "copying"
> by using the "getData() method" going on during the processing of
> methods such as add,subtract etc.
>
> getData()
>
http://jakarta.apache.org/commons/math/xref/org/apache/commons/math/linear/RealMatrixImpl.html#256
>
getData() is supposed to return a copy of the underlying data. That is
its contract.
>
> which calls copyOut(), copying the internal array just to access its
> contents
>
http://jakarta.apache.org/commons/math/xref/org/apache/commons/math/linear/RealMatrixImpl.html#821
>
>
> add()
>
http://jakarta.apache.org/commons/math/xref/org/apache/commons/math/linear/RealMatrixImpl.html#141
>
Yes, that should be fixed. getDataRef should be used in place of getData
to get the data for the instance.
>
> This seems unnecessary, I think using methods to access the array
> contents of the operand matrix would alleviate this unneeded copying.
> For instance:
>
>> for (int row = 0; row < rowCount; row++) {
>> for (int col = 0; col < columnCount; col++) {
>> outData[row][col] = data[row][col] + m.getEntry(row,col);
>> }
>> }
>
That would work in the current impl, actually even better than using
getDataRef.
>
> The modifications I am working on include these fixes and produce a
> separate abstract class "AbstractRealMatrix" which supports "storage
> independent" versions of these methods. I'm working to use this Abstract
> implementation to form the basis for RealMatrixImpl and any
> "internalized" versions used to support the column, Row and Submatrices.
Do we really need this? Do we need it for 1.0? Please provide more details.
>
Phil
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