[OpenVINO backend] Implements Fourier Transform operation istft()

[goyaladitya05]

Implements istft for the OpenVINO backend via a overlap and add approach using OpenVINO ops, mirroring the JAX/Torch reshape trick.

Added _overlap_sequences_ov helper that handles dynamic num_sequences via shape_of/gather ops.
Removed relevent tests from excluded_concrete_tests.txt.

Closes: openvinotoolkit/openvino/issues/34418

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the OpenVINO backend by providing a complete implementation of the Inverse Short-Time Fourier Transform (ISTFT) operation. This addition allows for the reconstruction of time-domain signals from their frequency-domain representations, mirroring established approaches in other backends like JAX and Torch. The implementation leverages OpenVINO's native operations for dynamic shape handling and efficient computation, making the backend more capable for audio and signal processing tasks.

Highlights

• Inverse Short-Time Fourier Transform (ISTFT) Implementation: The istft operation has been fully implemented for the OpenVINO backend, replacing the previous NotImplementedError. This enables the inverse transformation of STFT results within the OpenVINO environment.
• Overlap and Add Helper Function: A new helper function, _overlap_sequences_ov, was introduced to manage the overlap and add process crucial for istft. This function handles dynamic sequence numbers using OpenVINO's shape manipulation operations.
• Test Suite Updates: Relevant istft tests were removed from excluded_concrete_tests.txt, indicating that the newly implemented istft functionality is now expected to pass these tests.

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Changelog

• keras/src/backend/openvino/excluded_concrete_tests.txt
  • Removed multiple MathOpsCorrectnessTest::test_istft entries, indicating the istft operation is now supported.
• keras/src/backend/openvino/math.py
  • Added the _overlap_sequences_ov helper function to facilitate the overlap and add logic for ISTFT.
  • Implemented the istft function, including windowing, padding, inverse FFT, and dynamic shape handling using OpenVINO operations.
  • Replaced the NotImplementedError for istft with the full functional implementation.

Activity

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[gemini-code-assist]

Code Review

This pull request implements the istft operation for the OpenVINO backend. The implementation includes a new helper function _overlap_sequences_ov to perform the overlap-and-add method using OpenVINO operations. The changes look good overall. I've added a couple of suggestions to improve the readability and maintainability of the new code, mainly by using more descriptive variable names, adding comments to a complex function, and replacing a magic number with a named constant.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.58333% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.91%. Comparing base (f02d82b) to head (9363303).

Files with missing lines	Patch %	Lines
keras/src/backend/openvino/math.py	89.58%	3 Missing and 7 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #22323   +/-   ##
=======================================
  Coverage   82.90%   82.91%           
=======================================
  Files         594      594           
  Lines       65844    65940   +96     
  Branches    10293    10310   +17     
=======================================
+ Hits        54590    54676   +86     
- Misses       8638     8641    +3     
- Partials     2616     2623    +7     

Flag	Coverage Δ
keras	82.74% <89.58%> (+<0.01%)	⬆️
keras-jax	60.86% <2.08%> (-0.09%)	⬇️
keras-numpy	55.03% <0.00%> (-0.08%)	⬇️
keras-openvino	49.15% <89.58%> (+0.06%)	⬆️
keras-tensorflow	62.07% <2.08%> (-0.09%)	⬇️
keras-torch	60.93% <2.08%> (-0.09%)	⬇️

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[hertschuh]

Thanks for implementing these!