class_docstr: This class implements special functions using high-level code.
  
  Elementary and some other functions (e.g. gamma function, basecase
  hypergeometric series) are assumed to be predefined by the context as
  "builtins" or "low-level" functions.
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code: def _ei(ctx, z):
      raise NotImplementedError
  
imports: from ..libmp.backend import xrange
  import math
  import cmath
label_desc: Use image node_id 10 for calling the SpecialFunctions obj's underlying member method code with example usage: obj._ei(ctx, z) without return types