code: def autocovariance(input, dim=0):
      """
      Computes the autocovariance of samples at dimension ``dim``.
  
      :param torch.Tensor input: the input tensor.
      :param int dim: the dimension to calculate autocorrelation.
      :returns torch.Tensor: autocorrelation of ``input``.
      """
      return autocorrelation(input, dim) * input.var(
          dim, unbiased=False, keepdim=True
      )
  
imports: import math
  import numbers
  import torch
  from torch.fft import irfft, rfft
  from .tensor_utils import next_fast_len
label_desc: Use image node_id 5 for calling a global function with example usage: autocovariance(input, dim) and returns: unknown