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From "Jake Mannix (JIRA)" <j...@apache.org>
Subject [jira] Created: (MATH-316) Perf improvement: ArrayRealVector makes superfluous copies and often doesn't optimally operate on array values
Date Mon, 02 Nov 2009 17:48:59 GMT
Perf improvement: ArrayRealVector makes superfluous copies and often doesn't optimally operate
on array values
--------------------------------------------------------------------------------------------------------------

                 Key: MATH-316
                 URL: https://issues.apache.org/jira/browse/MATH-316
             Project: Commons Math
          Issue Type: Improvement
    Affects Versions: 2.0
         Environment: all
            Reporter: Jake Mannix
            Priority: Minor
             Fix For: 2.1


As discussed in the mailing list, things like ArrayRealVector#add:
{code}
            double[] out = new double[data.length];
            for (int i = 0; i < data.length; i++) {
                out[i] = data[i] + v.getEntry(i);
            }
            return new ArrayRealVector(out);
{code}
can be improved in the inner loop by simply
{code}
            double[] out = out.clone();
            for (int i = 0; i < data.length; i++) {
                out[i] += v.getEntry(i);
            }
            return new ArrayRealVector(out);
{code}

Which cuts down on array accesses.

Even more importantly, the last return line should pass in the boolean false, for "shallow
copy", or else this whole temporary array is being copied again and then the original discarded.

{code}
  return new ArrayRealVector(out, false);
{code}

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