class_docstr: Generic 1D Kernel object.
  Can be constructed by selecting a standard named Kernel,
  or providing a lambda expression and domain.
  The domain allows some algorithms to run faster for finite domain kernels.
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docstr: Normalising constant for kernel (integral from -inf to inf)
code: def norm_const(self):
      """
      Normalising constant for kernel (integral from -inf to inf)
      """
      if self._normconst is None:
          if self.domain is None:
              quadres = scipy.integrate.quad(self._shape, -inf, inf)
          else:
              quadres = scipy.integrate.quad(
                  self._shape, self.domain[0], self.domain[1]
              )
          self._normconst = 1.0 / (quadres[0])
      return self._normconst
  
imports: from statsmodels.compat.python import lzip, lfilter
  import numpy
  import scipy.integrate
  from scipy.special import factorial
  from numpy import exp, multiply, square, divide, subtract, inf
label_desc: Use image node_id 12 for calling the CustomKernel obj's underlying member method code with example usage: obj.norm_const() and returns: self