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From "Sujit Pal (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-230) Implement Sparse Matrix Support
Date Tue, 02 Dec 2008 20:08:44 GMT

    [ https://issues.apache.org/jira/browse/MATH-230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12652487#action_12652487
] 

Sujit Pal commented on MATH-230:
--------------------------------

Based on conversation with previous committers for the RealMatrixImpl code, I discovered that
I had accidentally removed some performance enhancement code. I have put this back in and
am resubmitting a fresh patch.

In addition to the changes described in the initial comment, the change here are:
1) Put back in the RealMatrixImpl.add(RealMatrixImpl), RealMatrixImpl.subtract(RealMatrixImpl)
and RealMatrixImpl.multiply(RealMatrixImpl) methods. These are now private methods since they
are meant to be used by the class itself for performance. Having them be public meant that
subclasses would use these instead its own overriden API methods, because the subclasses of
RealMatrixImpl is also a RealMatrixImpl, and thus a better match than a RealMatrix.
2) Add back the code which delegates to this method from RealMatrixImpl.add(RealMatrix), RealMatrixImpl.subtract(RealMatrix)
and RealMatrixImpl.multiply(RealMatrix). Instead of the try {} catch (ClassCastException)
{}, it is now using a if (RealMatrixImpl.class.equals(m.getClass()) {} else {} block to get
around the fact that subclasses are also RealMatrixImpl and hence are chosen in the try block.


> Implement Sparse Matrix Support
> -------------------------------
>
>                 Key: MATH-230
>                 URL: https://issues.apache.org/jira/browse/MATH-230
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 2.0
>         Environment: N/A
>            Reporter: Sujit Pal
>            Priority: Minor
>             Fix For: 2.0
>
>
> I needed a way to deal with large sparse matrices using commons-math RealMatrix, so I
implemented it. The SparseRealMatrixImpl is a subclass of RealMatrixImpl, and the backing
data structure is a Map<Point,Double>, where Point is a struct like inner-class which
exposes two int parameters row and column. I had to make some changes to the existing components
to keep the code for SparseRealMatrixImpl clean. Here are the details.
> 1) RealMatrix.java:
>    - added a new method setEntry(int, int, double) to set data into a matrix
> 2) RealMatrixImpl.java:
>    - changed all internal calls to data[i][j] to getEntry(i,j).
>    - for some methods such as add(), subtract(), premultiply(), etc, there
>      was code that checked for ClassCastException and had two versions,
>      one for a generic RealMatrix and one for a RealMatrixImpl. This has
>      been changed to have only one that operates on a RealMatrix. The 
>      result is something like auto-type casting. So if:
>        RealMatrixImpl.add(RealMatrix) returns a RealMatrixImpl
>        SparseRealMatrixImpl.add(RealMatrix) returns a SparseRealMatrixImpl
> 3) SparseRealMatrixImpl added as a subclass of RealMatrixImpl.
> 4) LUDecompositionImpl changed to use a clone of the passed in RealMatrix
>    instead of its data[][] block, and now it uses clone.getEntry(row,col)
>    calls instead of data[row][col] calls.
> 5) LUDecompositionImpl returned RealMatrixImpl for getL(), getU(), getP()
>    and solve(). It now returns the same RealMatrix impl that is passed 
>    in through its constructor for these methods.
> 6) New test for SparseRealMatrixImpl, mimics the tests in RealMatrixImplTest,
> 7) New static method to create SparseRealMatrixImpl out of a double[][] in
>    MatrixUtils.createSparseRealMatrix().
>    but using SparseRealMatrixImpl.
> 8) Verified that all JUnit tests pass.

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