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

["Jake Mannix (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MATH-316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12794777#action_12794777 ] 

Jake Mannix commented on MATH-316:
----------------------------------

Is the proper copy part of this fixed?

I still see in trunk places where we 
{code}
  double[] out = // stuff      
  return new ArrayRealVector(out);
{code}

instead of 

{code}
  double[] out = // stuff
  return new ArrayRealVector(out, false);
{code}

The default behavior for ArrayRealVector is to deep copy arrays passed in, which needs to be overridden here, no?

See ArrayRealVector.add,  ArrayRealVector.subtract, in particular.  I didn't pick through to see if this caught all of them.

It's entirely possible this was my fault and I missed them in my patches for the other issues which covered some of this.

> 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
>
>         Attachments: MATH-316.patch
>
>
> 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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