class_docstr: Vector function and its derivatives.
  
  This class defines a vector function F: R^n->R^m and methods for
  computing or approximating its first and second derivatives.
  
  Notes
  -----
  This class implements a memoization logic. There are methods `fun`,
  `jac`, hess` and corresponding attributes `f`, `J` and `H`. The following
  things should be considered:
  
      1. Use only public methods `fun`, `jac` and `hess`.
      2. After one of the methods is called, the corresponding attribute
         will be set. However, a subsequent call with a different argument
         of *any* of the methods may overwrite the attribute.
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code: def _update_fun(self):
      if not self.f_updated:
          self._update_fun_impl()
          self.f_updated = True
  
imports: from __future__ import division, print_function, absolute_import
  import numpy
  import scipy.sparse
  from ._numdiff import approx_derivative, group_columns
  from ._hessian_update_strategy import HessianUpdateStrategy
  from scipy.sparse.linalg import LinearOperator
label_desc: Use image node_id 4 for calling the VectorFunction obj's underlying member method code with example usage: obj._update_fun() without return types