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https://issues.apache.org/jira/browse/MATH-230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12656396#action_12656396
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Ismael Juma commented on MATH-230:
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Thanks for committing this Luc. Good point about specialised implementations of
add and subtract. However, the current implementation has a lot of overhead due
to the allocation of Entry objects. Since the iterator doesn't implement
java.util.Iterator anyway, we can do better by using an iterator similar to
Trove's. I will paste part of the javadoc below:
{code:java}
/**
* Iterator for maps of type int and double.
*
* <p>The iterator semantics for Trove's primitive maps is slightly different
* from those defined in <tt>java.util.Iterator</tt>, but still well within
* the scope of the pattern, as defined by Gamma, et al.</p>
*
* <p>This iterator does <b>not</b> implicitly advance to the next entry when
* the value at the current position is retrieved. Rather, you must explicitly
* ask the iterator to <tt>advance()</tt> and then retrieve either the
<tt>key()</tt>,
* the <tt>value()</tt> or both. This is done so that you have the option, but
not
* the obligation, to retrieve keys and/or values as your application requires,
and
* without introducing wrapper objects that would carry both. As the iteration
is
* stateful, access to the key/value parts of the current map entry happens in
* constant time.</p>
*
* <p>In practice, the iterator is akin to a "search finger" that you move from
* position to position. Read or write operations affect the current entry
only and
* do not assume responsibility for moving the finger.</p>
*
* <p>Here are some sample scenarios for this class of iterator:</p>
*
* <pre>
* // accessing keys/values through an iterator:
* for (TIntDoubleIterator it = map.iterator();
* it.hasNext();) {
* it.advance();
* if (satisfiesCondition(it.key()) {
* doSomethingWithValue(it.value());
* }
* }
* (snipped)
*/
Shall I file a separate issue for that?
> 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: math-230.diff, patch-2.txt,
> RealMatrixImplPerformanceTest.java, SparseRealMatrix.java,
> SparseRealMatrixTest.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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