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From "Sujit Pal (JIRA)" <>
Subject [jira] Created: (MATH-230) Implement Sparse Matrix Support
Date Sun, 30 Nov 2008 20:17:44 GMT
Implement Sparse Matrix Support

                 Key: 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.

   - added a new method setEntry(int, int, double) to set data into a matrix
   - 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
   but using SparseRealMatrixImpl.
8) Verified that all JUnit tests pass.

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