internal/ceres/linear_solver.h - ceres-solver - Git at Google

 // Ceres Solver - A fast non-linear least squares minimizer
 // Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
 // http://code.google.com/p/ceres-solver/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // * Redistributions of source code must retain the above copyright notice,
 //   this list of conditions and the following disclaimer.
 // * Redistributions in binary form must reproduce the above copyright notice,
 //   this list of conditions and the following disclaimer in the documentation
 //   and/or other materials provided with the distribution.
 // * Neither the name of Google Inc. nor the names of its contributors may be
 //   used to endorse or promote products derived from this software without
 //   specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 // POSSIBILITY OF SUCH DAMAGE.
 //
 // Author: sameeragarwal@google.com (Sameer Agarwal)
 //
 // Abstract interface for objects solving linear systems of various
 // kinds.

 #ifndef CERES_INTERNAL_LINEAR_SOLVER_H_
 #define CERES_INTERNAL_LINEAR_SOLVER_H_

 #include <cstddef>

 #include <glog/logging.h>
 #include "ceres/block_sparse_matrix.h"
 #include "ceres/casts.h"
 #include "ceres/compressed_row_sparse_matrix.h"
 #include "ceres/dense_sparse_matrix.h"
 #include "ceres/triplet_sparse_matrix.h"
 #include "ceres/types.h"

 namespace ceres {
 namespace internal {

 class LinearOperator;

 // Abstract base class for objects that implement algorithms for
 // solving linear systems
 //
 //   Ax = b
 //
 // It is expected that a single instance of a LinearSolver object
 // maybe used multiple times for solving different linear
 // systems. This allows them to cache and reuse information across
 // solves if for example the sparsity of the linear system remains
 // constant.
 //
 // Subclasses of LinearSolver use two structs to configure themselves.
 // The Options struct configures the LinearSolver object for its
 // lifetime. The PerSolveOptions struct is used to specify options for
 // a particular Solve call.
 class LinearSolver {
  public:
   struct Options {
     Options()
         : type(SPARSE_NORMAL_CHOLESKY),
           preconditioner_type(JACOBI),
           min_num_iterations(1),
           max_num_iterations(1),
           num_threads(1),
           constant_sparsity(false),
           num_eliminate_blocks(0),
           residual_reset_period(10),
           row_block_size(Dynamic),
           e_block_size(Dynamic),
           f_block_size(Dynamic) {
     }

     LinearSolverType type;

     PreconditionerType preconditioner_type;

     // Number of internal iterations that the solver uses. This
     // parameter only makes sense for iterative solvers like CG.
     int min_num_iterations;
     int max_num_iterations;

     // If possible, how many threads can the solver use.
     int num_threads;

     // If possible cache and reuse the symbolic factorization across
     // multiple calls.
     bool constant_sparsity;

     // Eliminate 0 to num_eliminate_blocks - 1 from the Normal
     // equations to form a schur complement. Only used by the Schur
     // complement based solver. The most common use for this parameter
     // is in the case of structure from motion problems where we have
     // camera blocks and point blocks. Then setting the
     // num_eliminate_blocks to the number of points allows the solver
     // to use the Schur complement trick. For more details see the
     // description of this parameter in solver.h.
     int num_eliminate_blocks;

     // Iterative solvers, e.g. Preconditioned Conjugate Gradients
     // maintain a cheap estimate of the residual which may become
     // inaccurate over time. Thus for non-zero values of this
     // parameter, the solver can be told to recalculate the value of
     // the residual using a |b - Ax| evaluation.
     int residual_reset_period;

     // If the block sizes in a BlockSparseMatrix are fixed, then in
     // some cases the Schur complement based solvers can detect and
     // specialize on them.
     //
     // It is expected that these parameters are set programmatically
     // rather than manually.
     //
     // Please see explicit_schur_complement_solver_impl.h for more
     // details.
     int row_block_size;
     int e_block_size;
     int f_block_size;
   };

   // Options for the Solve method.
   struct PerSolveOptions {
     PerSolveOptions()
         : D(NULL),
           preconditioner(NULL),
           r_tolerance(0.0),
           q_tolerance(0.0) {
     }

     // This option only makes sense for unsymmetric linear solvers
     // that can solve rectangular linear systems.
     //
     // Given a matrix A, an optional diagonal matrix D as a vector,
     // and a vector b, the linear solver will solve for
     //
     //   | A | x = | b |
     //   | D |     | 0 |
     //
     // If D is null, then it is treated as zero, and the solver returns
     // the solution to
     //
     //   A x = b
     //
     // In either case, x is the vector that solves the following
     // optimization problem.
     //
     //   arg min_x ||Ax - b||^2 + ||Dx||^2
     //
     // Here A is a matrix of size m x n, with full column rank. If A
     // does not have full column rank, the results returned by the
     // solver cannot be relied on. D, if it is not null is an array of
     // size n.  b is an array of size m and x is an array of size n.
     double * D;

     // This option only makes sense for iterative solvers.
     //
     // In general the performance of an iterative linear solver
     // depends on the condition number of the matrix A. For example
     // the convergence rate of the conjugate gradients algorithm
     // is proportional to the square root of the condition number.
     //
     // One particularly useful technique for improving the
     // conditioning of a linear system is to precondition it. In its
     // simplest form a preconditioner is a matrix M such that instead
     // of solving Ax = b, we solve the linear system AM^{-1} y = b
     // instead, where M is such that the condition number k(AM^{-1})
     // is smaller than the conditioner k(A). Given the solution to
     // this system, x = M^{-1} y. The iterative solver takes care of
     // the mechanics of solving the preconditioned system and
     // returning the corrected solution x. The user only needs to
     // supply a linear operator.
     //
     // A null preconditioner is equivalent to an identity matrix being
     // used a preconditioner.
     LinearOperator* preconditioner;


     // The following tolerance related options only makes sense for
     // iterative solvers. Direct solvers ignore them.

     // Solver terminates when
     //
     //   |Ax - b| <= r_tolerance * |b|.
     //
     // This is the most commonly used termination criterion for
     // iterative solvers.
     double r_tolerance;

     // For PSD matrices A, let
     //
     //   Q(x) = x'Ax - 2b'x
     //
     // be the cost of the quadratic function defined by A and b. Then,
     // the solver terminates at iteration i if
     //
     //   i * (Q(x_i) - Q(x_i-1)) / Q(x_i) < q_tolerance.
     //
     // This termination criterion is more useful when using CG to
     // solve the Newton step. This particular convergence test comes
     // from Stephen Nash's work on truncated Newton
     // methods. References:
     //
     //   1. Stephen G. Nash & Ariela Sofer, Assessing A Search
     //      Direction Within A Truncated Newton Method, Operation
     //      Research Letters 9(1990) 219-221.
     //
     //   2. Stephen G. Nash, A Survey of Truncated Newton Methods,
     //      Journal of Computational and Applied Mathematics,
     //      124(1-2), 45-59, 2000.
     //
     double q_tolerance;
   };

   // Summary of a call to the Solve method. We should move away from
   // the true/false method for determining solver success. We should
   // let the summary object do the talking.
   struct Summary {
     Summary()
         : residual_norm(0.0),
           num_iterations(-1),
           termination_type(FAILURE) {
     }

     double residual_norm;
     int num_iterations;
     LinearSolverTerminationType termination_type;
   };

   virtual ~LinearSolver();

   // Solve Ax = b.
   virtual Summary Solve(LinearOperator* A,
                         const double* b,
                         const PerSolveOptions& per_solve_options,
                         double* x) = 0;

   static LinearSolver* Create(const Options& options);
 };

 // This templated subclass of LinearSolver serves as a base class for
 // other linear solvers that depend on the particular matrix layout of
 // the underlying linear operator. For example some linear solvers
 // need low level access to the TripletSparseMatrix implementing the
 // LinearOperator interface. This class hides those implementation
 // details behind a private virtual method, and has the Solve method
 // perform the necessary upcasting.
 template <typename MatrixType>
 class TypedLinearSolver : public LinearSolver {
  public:
   virtual ~TypedLinearSolver() {}
   virtual LinearSolver::Summary Solve(
       LinearOperator* A,
       const double* b,
       const LinearSolver::PerSolveOptions& per_solve_options,
       double* x) {
     CHECK_NOTNULL(A);
     CHECK_NOTNULL(b);
     CHECK_NOTNULL(x);
     return SolveImpl(down_cast<MatrixType*>(A), b, per_solve_options, x);
   }

  private:
   virtual LinearSolver::Summary SolveImpl(
       MatrixType* A,
       const double* b,
       const LinearSolver::PerSolveOptions& per_solve_options,
       double* x) = 0;
 };

 // Linear solvers that depend on acccess to the low level structure of
 // a SparseMatrix.
 typedef TypedLinearSolver<BlockSparseMatrix>         BlockSparseMatrixSolver;          // NOLINT
 typedef TypedLinearSolver<BlockSparseMatrixBase>     BlockSparseMatrixBaseSolver;      // NOLINT
 typedef TypedLinearSolver<CompressedRowSparseMatrix> CompressedRowSparseMatrixSolver;  // NOLINT
 typedef TypedLinearSolver<DenseSparseMatrix>         DenseSparseMatrixSolver;          // NOLINT
 typedef TypedLinearSolver<TripletSparseMatrix>       TripletSparseMatrixSolver;        // NOLINT

 }  // namespace internal
 }  // namespace ceres

 #endif  // CERES_INTERNAL_LINEAR_SOLVER_H_
	// Ceres Solver - A fast non-linear least squares minimizer
	// Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
	// http://code.google.com/p/ceres-solver/
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// * Redistributions of source code must retain the above copyright notice,
	// this list of conditions and the following disclaimer.
	// * Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	// * Neither the name of Google Inc. nor the names of its contributors may be
	// used to endorse or promote products derived from this software without
	// specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
	// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	// POSSIBILITY OF SUCH DAMAGE.
	//
	// Author: sameeragarwal@google.com (Sameer Agarwal)
	//
	// Abstract interface for objects solving linear systems of various
	// kinds.

	#ifndef CERES_INTERNAL_LINEAR_SOLVER_H_
	#define CERES_INTERNAL_LINEAR_SOLVER_H_

	#include <cstddef>

	#include <glog/logging.h>
	#include "ceres/block_sparse_matrix.h"
	#include "ceres/casts.h"
	#include "ceres/compressed_row_sparse_matrix.h"
	#include "ceres/dense_sparse_matrix.h"
	#include "ceres/triplet_sparse_matrix.h"
	#include "ceres/types.h"

	namespace ceres {
	namespace internal {

	class LinearOperator;

	// Abstract base class for objects that implement algorithms for
	// solving linear systems
	//
	// Ax = b
	//
	// It is expected that a single instance of a LinearSolver object
	// maybe used multiple times for solving different linear
	// systems. This allows them to cache and reuse information across
	// solves if for example the sparsity of the linear system remains
	// constant.
	//
	// Subclasses of LinearSolver use two structs to configure themselves.
	// The Options struct configures the LinearSolver object for its
	// lifetime. The PerSolveOptions struct is used to specify options for
	// a particular Solve call.
	class LinearSolver {
	public:
	struct Options {
	Options()
	: type(SPARSE_NORMAL_CHOLESKY),
	preconditioner_type(JACOBI),
	min_num_iterations(1),
	max_num_iterations(1),
	num_threads(1),
	constant_sparsity(false),
	num_eliminate_blocks(0),
	residual_reset_period(10),
	row_block_size(Dynamic),
	e_block_size(Dynamic),
	f_block_size(Dynamic) {
	}

	LinearSolverType type;

	PreconditionerType preconditioner_type;

	// Number of internal iterations that the solver uses. This
	// parameter only makes sense for iterative solvers like CG.
	int min_num_iterations;
	int max_num_iterations;

	// If possible, how many threads can the solver use.
	int num_threads;

	// If possible cache and reuse the symbolic factorization across
	// multiple calls.
	bool constant_sparsity;

	// Eliminate 0 to num_eliminate_blocks - 1 from the Normal
	// equations to form a schur complement. Only used by the Schur
	// complement based solver. The most common use for this parameter
	// is in the case of structure from motion problems where we have
	// camera blocks and point blocks. Then setting the
	// num_eliminate_blocks to the number of points allows the solver
	// to use the Schur complement trick. For more details see the
	// description of this parameter in solver.h.
	int num_eliminate_blocks;

	// Iterative solvers, e.g. Preconditioned Conjugate Gradients
	// maintain a cheap estimate of the residual which may become
	// inaccurate over time. Thus for non-zero values of this
	// parameter, the solver can be told to recalculate the value of
	// the residual using a \|b - Ax\| evaluation.
	int residual_reset_period;

	// If the block sizes in a BlockSparseMatrix are fixed, then in
	// some cases the Schur complement based solvers can detect and
	// specialize on them.
	//
	// It is expected that these parameters are set programmatically
	// rather than manually.
	//
	// Please see explicit_schur_complement_solver_impl.h for more
	// details.
	int row_block_size;
	int e_block_size;
	int f_block_size;
	};

	// Options for the Solve method.
	struct PerSolveOptions {
	PerSolveOptions()
	: D(NULL),
	preconditioner(NULL),
	r_tolerance(0.0),
	q_tolerance(0.0) {
	}

	// This option only makes sense for unsymmetric linear solvers
	// that can solve rectangular linear systems.
	//
	// Given a matrix A, an optional diagonal matrix D as a vector,
	// and a vector b, the linear solver will solve for
	//
	// \| A \| x = \| b \|
	// \| D \| \| 0 \|
	//
	// If D is null, then it is treated as zero, and the solver returns
	// the solution to
	//
	// A x = b
	//
	// In either case, x is the vector that solves the following
	// optimization problem.
	//
	// arg min_x \|\|Ax - b\|\|^2 + \|\|Dx\|\|^2
	//
	// Here A is a matrix of size m x n, with full column rank. If A
	// does not have full column rank, the results returned by the
	// solver cannot be relied on. D, if it is not null is an array of
	// size n. b is an array of size m and x is an array of size n.
	double * D;

	// This option only makes sense for iterative solvers.
	//
	// In general the performance of an iterative linear solver
	// depends on the condition number of the matrix A. For example
	// the convergence rate of the conjugate gradients algorithm
	// is proportional to the square root of the condition number.
	//
	// One particularly useful technique for improving the
	// conditioning of a linear system is to precondition it. In its
	// simplest form a preconditioner is a matrix M such that instead
	// of solving Ax = b, we solve the linear system AM^{-1} y = b
	// instead, where M is such that the condition number k(AM^{-1})
	// is smaller than the conditioner k(A). Given the solution to
	// this system, x = M^{-1} y. The iterative solver takes care of
	// the mechanics of solving the preconditioned system and
	// returning the corrected solution x. The user only needs to
	// supply a linear operator.
	//
	// A null preconditioner is equivalent to an identity matrix being
	// used a preconditioner.
	LinearOperator* preconditioner;


	// The following tolerance related options only makes sense for
	// iterative solvers. Direct solvers ignore them.

	// Solver terminates when
	//
	// \|Ax - b\| <= r_tolerance * \|b\|.
	//
	// This is the most commonly used termination criterion for
	// iterative solvers.
	double r_tolerance;

	// For PSD matrices A, let
	//
	// Q(x) = x'Ax - 2b'x
	//
	// be the cost of the quadratic function defined by A and b. Then,
	// the solver terminates at iteration i if
	//
	// i * (Q(x_i) - Q(x_i-1)) / Q(x_i) < q_tolerance.
	//
	// This termination criterion is more useful when using CG to
	// solve the Newton step. This particular convergence test comes
	// from Stephen Nash's work on truncated Newton
	// methods. References:
	//
	// 1. Stephen G. Nash & Ariela Sofer, Assessing A Search
	// Direction Within A Truncated Newton Method, Operation
	// Research Letters 9(1990) 219-221.
	//
	// 2. Stephen G. Nash, A Survey of Truncated Newton Methods,
	// Journal of Computational and Applied Mathematics,
	// 124(1-2), 45-59, 2000.
	//
	double q_tolerance;
	};

	// Summary of a call to the Solve method. We should move away from
	// the true/false method for determining solver success. We should
	// let the summary object do the talking.
	struct Summary {
	Summary()
	: residual_norm(0.0),
	num_iterations(-1),
	termination_type(FAILURE) {
	}

	double residual_norm;
	int num_iterations;
	LinearSolverTerminationType termination_type;
	};

	virtual ~LinearSolver();

	// Solve Ax = b.
	virtual Summary Solve(LinearOperator* A,
	const double* b,
	const PerSolveOptions& per_solve_options,
	double* x) = 0;

	static LinearSolver* Create(const Options& options);
	};

	// This templated subclass of LinearSolver serves as a base class for
	// other linear solvers that depend on the particular matrix layout of
	// the underlying linear operator. For example some linear solvers
	// need low level access to the TripletSparseMatrix implementing the
	// LinearOperator interface. This class hides those implementation
	// details behind a private virtual method, and has the Solve method
	// perform the necessary upcasting.
	template <typename MatrixType>
	class TypedLinearSolver : public LinearSolver {
	public:
	virtual ~TypedLinearSolver() {}
	virtual LinearSolver::Summary Solve(
	LinearOperator* A,
	const double* b,
	const LinearSolver::PerSolveOptions& per_solve_options,
	double* x) {
	CHECK_NOTNULL(A);
	CHECK_NOTNULL(b);
	CHECK_NOTNULL(x);
	return SolveImpl(down_cast<MatrixType*>(A), b, per_solve_options, x);
	}

	private:
	virtual LinearSolver::Summary SolveImpl(
	MatrixType* A,
	const double* b,
	const LinearSolver::PerSolveOptions& per_solve_options,
	double* x) = 0;
	};

	// Linear solvers that depend on acccess to the low level structure of
	// a SparseMatrix.
	typedef TypedLinearSolver<BlockSparseMatrix> BlockSparseMatrixSolver; // NOLINT
	typedef TypedLinearSolver<BlockSparseMatrixBase> BlockSparseMatrixBaseSolver; // NOLINT
	typedef TypedLinearSolver<CompressedRowSparseMatrix> CompressedRowSparseMatrixSolver; // NOLINT
	typedef TypedLinearSolver<DenseSparseMatrix> DenseSparseMatrixSolver; // NOLINT
	typedef TypedLinearSolver<TripletSparseMatrix> TripletSparseMatrixSolver; // NOLINT

	} // namespace internal
	} // namespace ceres

	#endif // CERES_INTERNAL_LINEAR_SOLVER_H_