docstr: This function applies the softmax to the Periodic Kernel
  hyper-parameters.
  
  Parameters
  ----------
  F
      A module that can either refer to the Symbol API or the NDArray
      API in MXNet.
  amplitude
      Periodic kernel amplitude hyper-parameter of shape
      (batch_size, 1, 1).
  length_scale
      Periodic kernel length scale hyper-parameter of of shape
      (batch_size, 1, 1).
  frequency
      Periodic kernel hyper-parameter of shape (batch_size, 1, 1).
  
  Returns
  -------
  Tuple[Tensor, Tensor, Tensor]
      Three GP Periodic kernel hyper-parameters.
      Each is a Tensor of shape: (batch_size, 1, 1).
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code: def domain_map(cls, F, amplitude, length_scale, frequency):
      r"""
      This function applies the softmax to the Periodic Kernel
      hyper-parameters.
  
      Parameters
      ----------
      F
          A module that can either refer to the Symbol API or the NDArray
          API in MXNet.
      amplitude
          Periodic kernel amplitude hyper-parameter of shape
          (batch_size, 1, 1).
      length_scale
          Periodic kernel length scale hyper-parameter of of shape
          (batch_size, 1, 1).
      frequency
          Periodic kernel hyper-parameter of shape (batch_size, 1, 1).
  
      Returns
      -------
      Tuple[Tensor, Tensor, Tensor]
          Three GP Periodic kernel hyper-parameters.
          Each is a Tensor of shape: (batch_size, 1, 1).
      """
      amplitude = softplus(F, amplitude)
      length_scale = softplus(F, length_scale)
      frequency = softplus(F, frequency)
      return amplitude, length_scale, frequency
  
file_path: gluonts/src/gluonts/mx/kernels/_periodic_kernel.py
imports: import math
  from typing import Dict, Tuple
  from gluonts.mx import Tensor
  from gluonts.mx.distribution.distribution import getF, softplus
  from .None import Kernel, KernelOutputDict
label_desc: Use image node_id 2 for calling the PeriodicKernelOutput obj's underlying member method code with example usage: obj.domain_map(cls, F, amplitude, length_scale, frequency) and returns: amplitude,  length_scale,  frequency