Re: cvs commit: jakarta-commons/math/src/test/org/apache/commons/math/linear RealMatrixImplTest.java

[Phil Steitz]

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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