Hello,
Someone complained recently to me about poor performances of
RealMatrix.multiply(). A quick check showed me that changing the indices
checks in RealMatrix.getEntry() tremendously improved the performances
(about a 3 to 1 ratio in a simple case).
The current implementation explicitely calls the isValidCoordinate prior
to getting the element from the underlying array. This method calls
getRowDimension and getColumnDimension and do the intervals checks. I
think this is unnecessary and duplicates the checks that are already
done by the JVM. I would like to replace this by an a posteriori check
when the JVM triggers an ArrayIndexOutOfBoundException. Basically, this
means replacing:
if (!isValidCoordinate(row,column)) {
throw new MatrixIndexException(...);
}
return data[row][column];
by:
try {
return data[row][column];
} catch (ArrayIndexOutOfBoundsException e) {
throw new MatrixIndexException(...);
}
I have read somewhere that array index checking is now highly optimized
by JVM and can even be automatically removed in some cases. Do you think
moving to such a way to handle index errors is sensible ? There are
several other places where this could be done, so I would like to have
your comments before doing the changes.
Luc
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