code: def _cseries_to_zseries(c):
      """Convert Chebyshev series to z-series.
  
      Convert a Chebyshev series to the equivalent z-series. The result is
      never an empty array. The dtype of the return is the same as that of
      the input. No checks are run on the arguments as this routine is for
      internal use.
  
      Parameters
      ----------
      c : 1-D ndarray
          Chebyshev coefficients, ordered from low to high
  
      Returns
      -------
      zs : 1-D ndarray
          Odd length symmetric z-series, ordered from  low to high.
  
      """
      n = c.size
      zs = np.zeros(2 * n - 1, dtype=c.dtype)
      zs[n - 1 :] = c / 2
      return zs + zs[::-1]
  
imports: import numpy
  import numpy.linalg
  from numpy.core.multiarray import normalize_axis_index
  from .None import polyutils
  from ._polybase import ABCPolyBase
label_desc: Use image node_id 1 for calling a global function with example usage: _cseries_to_zseries(c) and returns: unknown