[jira] [Resolved] (MATH-732) Major Speed Improvement to 1D Discrete Fourier Transform (approximately 5x-9x improvement). Preserved public API 100%. Removed unnecessary use of instance variables and instance state.

["Sébastien Brisard (Resolved JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-732?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sébastien Brisard resolved MATH-732.
------------------------------------

    Resolution: Fixed

Patch successfully committed. Many thanks to the contributor. Further API changes are considered in MATH-743.
                
> Major Speed Improvement to 1D Discrete Fourier Transform (approximately 5x-9x improvement). Preserved public API 100%. Removed unnecessary use of instance variables and instance state.
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: MATH-732
>                 URL: https://issues.apache.org/jira/browse/MATH-732
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.0
>            Reporter: Kurt Ostfeld
>            Assignee: Sébastien Brisard
>              Labels: api, perfomance
>             Fix For: 3.0
>
>         Attachments: DFTPerformanceWithPatch.png, DFTPerformanceWithoutPatch.png, FastFourierTransformer.java, FastFourierTransformerTest.java, Main.java
>
>
> I wrote my own Discrete Fourier Transform function in Java and ran some benchmarks and found that it ran dramatically faster than the Apache library implementation. This is a pretty straight forward implementation of the standard Cooley Tukey algorithm that I read out of a textbook. This passes all the Apache library test cases plus several I had written on my own. I created a source code library patch that preserves the public API completely while changing the internal implementation to achieve the performance improvement.
> In addition to the performance issue, I suggest that Discrete Fourier Transform functionality be provided as stateless pure functions (in Java this would be implemented with static methods) just like most other math functions. As-is, the library requires the user to instantiate a Transformer instance which maintains instance state, which is an unecessary complexity for a pure math function. I held off on this change since it would change the public API and affect existing code. However, I see similar backward compatability breaking API changes are already in the FastFourierTransformer class in the 3.0 code base.

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