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  1. Commons Math
  2. 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.



    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 3.0
    • 3.0


      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.


        1. DFTPerformanceWithoutPatch.png
          8 kB
          Kurt Ostfeld
        2. DFTPerformanceWithPatch.png
          8 kB
          Kurt Ostfeld
        3. FastFourierTransformer.java
          31 kB
          Kurt Ostfeld
        4. FastFourierTransformerTest.java
          30 kB
          Kurt Ostfeld
        5. Main.java
          1 kB
          Kurt Ostfeld



            celestin Sebastien Brisard
            kurtostfeld Kurt Ostfeld
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