# scipy.optimize.HessianUpdateStrategy

class scipy.optimize.HessianUpdateStrategy

  Interface for implementing Hessian update strategies.

  Many optimization methods make use of Hessian (or inverse Hessian) approximations, such as the quasi-Newton methods BFGS, SR1, L-BFGS. Some of these approximations, however, do not actually need to store the entire matrix or can compute the internal matrix product with a given vector in a very efficiently manner. This class serves as an abstract interface between the optimization algorithm and the quasi-Newton update strategies, giving freedom of implementation to store and update the internal matrix as efficiently as possible. Different choices of initialization and update procedure will result in different quasi-Newton strategies.

  Four methods should be implemented in derived classes: `initialize`, `update`, `dot` and `get_matrix`.

  Notes

  Any instance of a class that implements this interface, can be accepted by the method `minimize` and used by the compatible solvers to approximate the Hessian (or inverse Hessian) used by the optimization algorithms.

  Methods

  `dot`(p) | Compute the product of the internal matrix with the given vector.
  `get_matrix`() | Return current internal matrix.
  `initialize`(n, approx_type) | Initialize internal matrix.
  `update`(delta_x, delta_grad) | Update internal matrix.