code: def sos2tf(sos):
      """
      Return a single transfer function from a series of second-order sections
  
      Parameters
      ----------
      sos : array_like
          Array of second-order filter coefficients, must have shape
          ``(n_sections, 6)``. See `sosfilt` for the SOS filter format
          specification.
  
      Returns
      -------
      b : ndarray
          Numerator polynomial coefficients.
      a : ndarray
          Denominator polynomial coefficients.
  
      See Also
      --------
      scipy.signal.sos2tf
  
      """
      sos = cupy.asarray(sos)
      result_type = sos.dtype
      if result_type.kind in "bui":
          result_type = cupy.float64
  
      b = cupy.array([1], dtype=result_type)
      a = cupy.array([1], dtype=result_type)
      n_sections = sos.shape[0]
      for section in range(n_sections):
          b = cupy.polymul(b, sos[section, :3])
          a = cupy.polymul(a, sos[section, 3:])
      return b, a
  
imports: import warnings
  import math
  from math import pi, prod
  import cupy
  from cupyx.scipy.special import binom
  import cupyx.scipy.special
  from cupyx.scipy.signal import _optimize
  from cupyx.scipy.signal._polyutils import roots, poly
  from cupyx.scipy.signal._lti_conversion import abcd_normalize
label_desc: Use image node_id 23 for calling a global function with example usage: sos2tf(sos) and returns: b,  a