class_docstr: Riemann Xi function.
  
  Examples
  ========
  
  The Riemann Xi function is closely related to the Riemann zeta function.
  The zeros of Riemann Xi function are precisely the non-trivial zeros
  of the zeta function.
  
  >>> from sympy import riemann_xi, zeta
  >>> from sympy.abc import s
  >>> riemann_xi(s).rewrite(zeta)
  s*(s - 1)*gamma(s/2)*zeta(s)/(2*pi**(s/2))
  
  References
  ==========
  
  .. [1] https://en.wikipedia.org/wiki/Riemann_Xi_function
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code: def eval(cls, s):
      from sympy.functions.special.gamma_functions import gamma
  
      z = zeta(s)
      if s in (S.Zero, S.One):
          return S.Half
  
      if not isinstance(z, zeta):
          return s * (s - 1) * gamma(s / 2) * z / (2 * pi ** (s / 2))
  
imports: from sympy.core.add import Add
  from sympy.core.cache import cacheit
  from sympy.core.function import ArgumentIndexError, expand_mul, Function
  from sympy.core.numbers import pi, I, Integer
  from sympy.core.relational import Eq
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy
  from sympy.core.sympify import sympify
  from sympy.functions.combinatorial.numbers import bernoulli, factorial, genocchi, harmonic
  from sympy.functions.elementary.complexes import re, unpolarify, Abs, polar_lift
  from sympy.functions.elementary.exponential import log, exp_polar, exp
  from sympy.functions.elementary.integers import ceiling, floor
  from sympy.functions.elementary.miscellaneous import sqrt
  from sympy.functions.elementary.piecewise import Piecewise
  from sympy.polys.polytools import Poly
label_desc: Use image node_id 1 for calling the riemann_xi obj's underlying member method code with example usage: obj.eval(cls, s) and returns: S, unknown