code: def FFT_for_Period(x, k=2):
      # [B, T, C]
      xf = torch.fft.rfft(x, dim=1)
      # find period by amplitudes
      frequency_list = abs(xf).mean(0).mean(-1)
      frequency_list[0] = 0
      _, top_list = torch.topk(frequency_list, k)
      top_list = top_list.detach().cpu().numpy()
      period = x.shape[1] // top_list
      return period, abs(xf).mean(-1)[:, top_list]
  
imports: from typing import Optional
  import torch
  import torch.nn
  import torch.nn.functional
  import torch.fft
  from ..common._modules import DataEmbedding
  from ..common._base_windows import BaseWindows
  from ..losses.pytorch import MAE
label_desc: Use image node_id 1 for calling a global function with example usage: FFT_for_Period(x, k) and returns: period,  abs