code: def _fft(x: np.ndarray, fft_length: int, axis: int) -> np.ndarray:
      """Compute the FFT return the real representation of the complex result."""
      transformed = np.fft.fft(x, n=fft_length, axis=axis)
      real_frequencies = np.real(transformed)
      imaginary_frequencies = np.imag(transformed)
      return np.concatenate(
          (
              real_frequencies[..., np.newaxis],
              imaginary_frequencies[..., np.newaxis],
          ),
          axis=-1,
      )
  
file_path: onnx/onnx/reference/ops/op_dft.py
imports: from __future__ import annotations
  import numpy
  from onnx.reference.op_run import OpRun
label_desc: Use image node_id 1 for calling a global function with example usage: _fft(x, fft_length, axis) and returns: np