code: def _anticausal_init_code(mode):
      """Code for the anti-causal initialization step of IIR filtering.
  
      c is a 1d array of length n and z is a filter pole
      """
      code = f"""
          // anti-causal init for mode={mode}"""
      if mode == "mirror":
          code += """
          c[(n - 1) * element_stride] = (
              z * c[(n - 2) * element_stride] +
              c[(n - 1) * element_stride]) * z / (z * z - 1);"""
      elif mode == "grid-wrap":
          code += """
          z_i = z;
  
          for (i = 0; i < min(n - 1, static_cast<idx_t>({n_boundary})); ++i) {{
              c[(n - 1) * element_stride] += z_i * c[i * element_stride];
              z_i *= z;
          }}
          c[(n - 1) * element_stride] *= z / (z_i - 1); /* z_i = pow(z, n) */"""
      elif mode == "reflect":
          code += """
          c[(n - 1) * element_stride] *= z / (z - 1);"""
      else:
          raise ValueError("invalid mode: {}".format(mode))
      return code
  
file_path: cupy/cupyx/scipy/ndimage/_spline_prefilter_core.py
imports: import functools
  import math
  import operator
  import textwrap
  import cupy
label_desc: Use image node_id 4 for calling a global function with example usage: _anticausal_init_code(mode) and returns: code