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From Sébastien Brisard (Commented) (JIRA) <j...@apache.org>
Subject [jira] [Commented] (MATH-743) Use enums in package transform
Date Fri, 10 Feb 2012 08:55:59 GMT

    [ https://issues.apache.org/jira/browse/MATH-743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13205295#comment-13205295
] 

Sébastien Brisard commented on MATH-743:
----------------------------------------

In revision {{r1242703}}, introduced
* enumeration {{TransformType}}, with two values {{FORWARD}} and {{INVERSE}}
* enumeration {{FastFourierTransformer.DftNormalization}}, with two values {{STANDARD}} and
{{UNITARY}}.

In {{FastFourierTransformer}}, the normalization is now specified at construction time, while
the type is specified in the methods {{Complex[] transform(Complex[], TransformType)}} and
the likes. The rationale is that no matter the transform (DFT, DST, DCT, DHT), forward and
inverse are always meaningful (so {{TransformType}} is shared by *all* transforms). On the
other hand, normalization is transform specific. For example, DST and DCT can be made orthogonal,
while FFT can be made unitary (orthogonal doesn't mean anything with complex transforms).

This API change greatly simplifies unit testing, as it is now possible to *loop* over the
types and normalizations!

In order to allow for possible independent implementations of the DFT, I propose that {{DftNormalization}}
be a top-level enum, instead of a nested enum. Also, most of the header of the current Javadoc
of {{FastFourierTransformer}} should actually move to {{DftNormalization}}.
                
> Use enums in package transform
> ------------------------------
>
>                 Key: MATH-743
>                 URL: https://issues.apache.org/jira/browse/MATH-743
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.0
>            Reporter: Sébastien Brisard
>            Assignee: Sébastien Brisard
>              Labels: api-change, enum, transform
>
> As discussed on the mailing-list, enums could be used in the package {{transform}}
> # An enumeration {{FORWARD, INVERSE}} will be created to specify whether the inverse
transform is to be computed. This will replace the pair {{transform}}/{{inverseTransform}}
> # An enumeration {{STANDARD, ORTHOGONAL}} will be introduced (where relevant) in each
transform class, in order to specify the normalization that should be used. Then the factory
methods {{create()}}/{{createOrthogonal()}} will be replaced by a parameter passed to the
constructor, which will be made public.

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