[jira] [Commented] (MATH-879) "CMAESOptimizer" silently changes invalid input

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

    [ https://issues.apache.org/jira/browse/MATH-879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13479013#comment-13479013 ] 

Gilles commented on MATH-879:
-----------------------------

The code is:
{code}
if (lambda <= 0) {
  lambda = 4 + (int) (3 * Math.log(dimension));
}
{code}

This implies that the default is dependent on the number of optimized parameters. Hence, I would suggest that "lambda" be specified at the call to "optimize", as kind of "OptimizationData" (with a more suggestive name, such as "PopulationSize"), with no default (the value currently used in the code could appear as a _suggestion_ in the documentation).
And passing this parameter through the constructor will be deprecated.

What do you think?

                
> "CMAESOptimizer" silently changes invalid input
> -----------------------------------------------
>
>                 Key: MATH-879
>                 URL: https://issues.apache.org/jira/browse/MATH-879
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Gilles
>            Assignee: Gilles
>            Priority: Trivial
>             Fix For: 3.1
>
>
> The "lambda" input parameter must be strictly positive. But when it's not the case, an undocumented default is used (cf. line 526).
> When a precondition is not satisfied, the code must throw an exception.
> Instead of the code unknowingly changing the input, it is rather the documentation that should suggest a good default.
> This change would allow to make "lambda" a constant (final) field.

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