Brian created MATH-1170:
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Summary: Add more in-place operations to RealMatrix and RealVector
Key: MATH-1170
URL: https://issues.apache.org/jira/browse/MATH-1170
Project: Commons Math
Issue Type: Improvement
Reporter: Brian
Priority: Minor
It would be nice if for many methods of RealMatrix and RealVector there were
in-place versions of the methods - that would use the existing structures
rather than creating new ones. There are certain situations where this is
preferable. For example, a series of matrices all of which will operate on the
same vector, after transforming the result each time. This could be done very
frequently and the vector can be very large. In some situations it is
significantly more efficient to use the same vector instead of creating many
temporary ones each time which then have to be garbage collected.
An example of two methods that could benefit from in-place versions: the
RealMatrix.operate and RealVector.add. E.g., RealMatrix.operatInPlace, would
transform its input vector/double array without creating a new one.
There was also a question on stack overflow about this:
http://stackoverflow.com/questions/20529484/performing-in-place-calculations-with-commons-maths-realmatrix
There is also a lot of precedents for this kind of behavior, in other languages.
In other languages, this is sometimes handled behind the scenes - when a
self-assignment is found, a new variable is not created - in order to improve
performance. E.g., some functional languages perform such optimizations behind
the scenes, and it is used in MATLAB:
http://blogs.mathworks.com/loren/2007/03/22/in-place-operations-on-data/
http://undocumentedmatlab.com/blog/internal-matlab-memory-optimizations
In some ways directly providing the option for in-place operations is
preferable because then we could control when it is applied. It could be used
where appropriate within the internals of other methods as well.
Similarly there is also a convention in Ruby to have a special version of a
method, marked with a "!" to indicate it is "dangerous" - usually meaning it
changes its input - so-called "bang methods". Many of these are built into the
core Ruby, e.g., sort/sort! for arrays, upcase/upcase!, chomp/chomp!, and
reverse/reverse! for strings.
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