class_docstr: A kernel class. 
class_docstr_tok: ["A","kernel","class","."]
docstr: Evaluates the kernel by calling evaluate. 
docstr_tok: ["Evaluates","the","kernel","by","calling","evaluate","."]
code: def __call__(self, X1, X2=None):
      """Evaluates the kernel by calling evaluate."""
      return self.evaluate(X1, X2)
  
imports: from __future__ import print_function
  import numpy
  from scipy.linalg import solve_triangular
label_desc: Use image node_id 2 for calling the Kernel obj's underlying member method code with example usage: obj.__call__(X1, X2) and returns: self