1 // Ceres Solver - A fast non-linear least squares minimizer
2 // Copyright 2015 Google Inc. All rights reserved.
3 // http://ceres-solver.org/
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6 // modification, are permitted provided that the following conditions are met:
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9 // this list of conditions and the following disclaimer.
10 // * Redistributions in binary form must reproduce the above copyright notice,
11 // this list of conditions and the following disclaimer in the documentation
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15 // specific prior written permission.
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29 // Author: sameeragarwal@google.com (Sameer Agarwal)
31 #ifndef CERES_INTERNAL_DOGLEG_STRATEGY_H_
32 #define CERES_INTERNAL_DOGLEG_STRATEGY_H_
34 #include "ceres/linear_solver.h"
35 #include "ceres/trust_region_strategy.h"
40 // Dogleg step computation and trust region sizing strategy based on
41 // on "Methods for Nonlinear Least Squares" by K. Madsen, H.B. Nielsen
42 // and O. Tingleff. Available to download from
44 // http://www2.imm.dtu.dk/pubdb/views/edoc_download.php/3215/pdf/imm3215.pdf
46 // One minor modification is that instead of computing the pure
47 // Gauss-Newton step, we compute a regularized version of it. This is
48 // because the Jacobian is often rank-deficient and in such cases
49 // using a direct solver leads to numerical failure.
51 // If SUBSPACE is passed as the type argument to the constructor, the
52 // DoglegStrategy follows the approach by Shultz, Schnabel, Byrd.
53 // This finds the exact optimum over the two-dimensional subspace
54 // spanned by the two Dogleg vectors.
55 class DoglegStrategy : public TrustRegionStrategy {
57 explicit DoglegStrategy(const TrustRegionStrategy::Options& options);
58 virtual ~DoglegStrategy() {}
60 // TrustRegionStrategy interface
61 virtual Summary ComputeStep(const PerSolveOptions& per_solve_options,
62 SparseMatrix* jacobian,
63 const double* residuals,
65 virtual void StepAccepted(double step_quality);
66 virtual void StepRejected(double step_quality);
67 virtual void StepIsInvalid();
69 virtual double Radius() const;
71 // These functions are predominantly for testing.
72 Vector gradient() const { return gradient_; }
73 Vector gauss_newton_step() const { return gauss_newton_step_; }
74 Matrix subspace_basis() const { return subspace_basis_; }
75 Vector subspace_g() const { return subspace_g_; }
76 Matrix subspace_B() const { return subspace_B_; }
79 typedef Eigen::Matrix<double, 2, 1, Eigen::DontAlign> Vector2d;
80 typedef Eigen::Matrix<double, 2, 2, Eigen::DontAlign> Matrix2d;
82 LinearSolver::Summary ComputeGaussNewtonStep(
83 const PerSolveOptions& per_solve_options,
84 SparseMatrix* jacobian,
85 const double* residuals);
86 void ComputeCauchyPoint(SparseMatrix* jacobian);
87 void ComputeGradient(SparseMatrix* jacobian, const double* residuals);
88 void ComputeTraditionalDoglegStep(double* step);
89 bool ComputeSubspaceModel(SparseMatrix* jacobian);
90 void ComputeSubspaceDoglegStep(double* step);
92 bool FindMinimumOnTrustRegionBoundary(Vector2d* minimum) const;
93 Vector MakePolynomialForBoundaryConstrainedProblem() const;
94 Vector2d ComputeSubspaceStepFromRoot(double lambda) const;
95 double EvaluateSubspaceModel(const Vector2d& x) const;
97 LinearSolver* linear_solver_;
99 const double max_radius_;
101 const double min_diagonal_;
102 const double max_diagonal_;
104 // mu is used to scale the diagonal matrix used to make the
105 // Gauss-Newton solve full rank. In each solve, the strategy starts
106 // out with mu = min_mu, and tries values upto max_mu. If the user
107 // reports an invalid step, the value of mu_ is increased so that
108 // the next solve starts with a stronger regularization.
110 // If a successful step is reported, then the value of mu_ is
111 // decreased with a lower bound of min_mu_.
113 const double min_mu_;
114 const double max_mu_;
115 const double mu_increase_factor_;
116 const double increase_threshold_;
117 const double decrease_threshold_;
119 Vector diagonal_; // sqrt(diag(J^T J))
123 Vector gauss_newton_step_;
125 // cauchy_step = alpha * gradient
127 double dogleg_step_norm_;
129 // When, ComputeStep is called, reuse_ indicates whether the
130 // Gauss-Newton and Cauchy steps from the last call to ComputeStep
131 // can be reused or not.
133 // If the user called StepAccepted, then it is expected that the
134 // user has recomputed the Jacobian matrix and new Gauss-Newton
135 // solve is needed and reuse is set to false.
137 // If the user called StepRejected, then it is expected that the
138 // user wants to solve the trust region problem with the same matrix
139 // but a different trust region radius and the Gauss-Newton and
140 // Cauchy steps can be reused to compute the Dogleg, thus reuse is
143 // If the user called StepIsInvalid, then there was a numerical
144 // problem with the step computed in the last call to ComputeStep,
145 // and the regularization used to do the Gauss-Newton solve is
146 // increased and a new solve should be done when ComputeStep is
147 // called again, thus reuse is set to false.
150 // The dogleg type determines how the minimum of the local
151 // quadratic model is found.
152 DoglegType dogleg_type_;
154 // If the type is SUBSPACE_DOGLEG, the two-dimensional
155 // model 1/2 x^T B x + g^T x has to be computed and stored.
156 bool subspace_is_one_dimensional_;
157 Matrix subspace_basis_;
158 Vector2d subspace_g_;
159 Matrix2d subspace_B_;
162 } // namespace internal
165 #endif // CERES_INTERNAL_DOGLEG_STRATEGY_H_