code: def tf_solve(self, fn_x, x_init, b):
          
          return super(ConjugateGradient, self).tf_solve(fn_x, x_init, b)
docs: Iteratively solves the system of linear equations $A x = b$.
  
          Args:
              fn_x: A callable returning the left-hand side $A x$ of the system of linear equations.
              x_init: Initial solution guess $x_0$, zero vector if None.
              b: The right-hand side $b$ of the system of linear equations.
  
          Returns:
              A solution $x$ to the problem as given by the solver.