code: def wald_pdf(x):
      if x > 0:
          return math.exp(-((x - 1) ** 2) / (2 * x)) / math.sqrt(x**3)
      return 0.0
  
imports: import math
  import numbers
  import numpy
  from scipy import stats
  from scipy import special
  from ._qmc import check_random_state, Halton, QMCEngine
  from ._unuran.unuran_wrapper import NumericalInversePolynomial
  from scipy._lib._util import check_random_state
label_desc: Use image node_id 18 for calling a global function with example usage: wald_pdf(x) and returns: int, unknown