[MATH-316] Perf improvement: ArrayRealVector makes superfluous copies and often doesn't optimally operate on array values

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.0
• Fix Version/s: 2.1

Environment

all

• Assignee: Unassigned
• Reporter: Jake Mannix
• Created: 02/Nov/09 17:47
• Updated: 03/Apr/10 20:50
• Resolved: 27/Dec/09 20:21

Description

As discussed in the mailing list, things like ArrayRealVector#add:

            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);

can be improved in the inner loop by simply

            double[] out = out.clone();
            for (int i = 0; i < data.length; i++) {
                out[i] += v.getEntry(i);
            }
            return new ArrayRealVector(out);

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.

  return new ArrayRealVector(out, false);