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https://issues.apache.org/jira/browse/MATH-230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12653887#action_12653887
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Sujit Pal commented on MATH-230:
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>> Or we could just add the appropriate specialised Map to commons-math. Are
>> there objections to that?
I cannot answer this one, since I am not a developer on the project - my
observation is that there are no dependencies for this project save the JDK,
which leads me to believe that there may have been a concious decision to keep
it that way, but I could be wrong. As for adding it into commons-math, my
personal opinion is that it belongs in a data structure package such as
commons-collections or such, but thats just my view.
>> I think it's important to provide an implementation that has the right
>> performance characteristics
>> by default.
I completely agree. And the open/chained hashmap would definitely be more
appropriate in a memory constrained environment where a SparseMatrix would be
considered, than my Map<Point,Double>.
And if it is implemented as a private inner class, then it is visible only from
within the implementation, so I think there should be no issues. And it would
be completely justifiable, since we are basically creating a fast data
structure to serve the impl.
However, it is already assigned to be reviewed, so I am guessing that when Luc
gets to this bug, he will post his review. FWIW, I think that if we do end up
including the SparseMatrixImpl, then definitely your approach with the
open/chained hashmap would be preferable to the one thats in there. If you have
th bandwidth to build it, then I think it may be quite helpful.
> 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
> Assignee: Luc Maisonobe
> Priority: Minor
> Fix For: 2.0
>
> Attachments: patch.txt, RealMatrixImplPerformanceTest.java,
> SparseRealMatrixImpl.java, SparseRealMatrixImplTest.java
>
>
> 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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