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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// 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: sameragarwal@google.com (Sameer Agarwal)
+
+#ifndef CERES_INTERNAL_PREPROCESSOR_H_
+#define CERES_INTERNAL_PREPROCESSOR_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "ceres/coordinate_descent_minimizer.h"
+#include "ceres/evaluator.h"
+#include "ceres/internal/eigen.h"
+#include "ceres/internal/port.h"
+#include "ceres/iteration_callback.h"
+#include "ceres/linear_solver.h"
+#include "ceres/minimizer.h"
+#include "ceres/problem_impl.h"
+#include "ceres/program.h"
+#include "ceres/solver.h"
+
+namespace ceres {
+namespace internal {
+
+struct PreprocessedProblem;
+
+// Given a Problem object and a Solver::Options object indicating the
+// configuration of the solver, the job of the Preprocessor is to
+// analyze the Problem and perform the setup needed to solve it using
+// the desired Minimization algorithm. The setup involves removing
+// redundancies in the input problem (inactive parameter and residual
+// blocks), finding fill reducing orderings as needed, configuring and
+// creating various objects needed by the Minimizer to solve the
+// problem such as an evaluator, a linear solver etc.
+//
+// Each Minimizer (LineSearchMinimizer and TrustRegionMinimizer) comes
+// with a corresponding Preprocessor (LineSearchPreprocessor and
+// TrustRegionPreprocessor) that knows about its needs and performs
+// the preprocessing needed.
+//
+// The output of the Preprocessor is stored in a PreprocessedProblem
+// object.
+class Preprocessor {
+ public:
+  // Factory.
+  static Preprocessor* Create(MinimizerType minimizer_type);
+  virtual ~Preprocessor();
+  virtual bool Preprocess(const Solver::Options& options,
+                          ProblemImpl* problem,
+                          PreprocessedProblem* pp) = 0;
+};
+
+// A PreprocessedProblem is the result of running the Preprocessor on
+// a Problem and Solver::Options object.
+struct PreprocessedProblem {
+  PreprocessedProblem()
+      : fixed_cost(0.0) {
+  }
+
+  std::string error;
+  Solver::Options options;
+  LinearSolver::Options linear_solver_options;
+  Evaluator::Options evaluator_options;
+  Minimizer::Options minimizer_options;
+
+  ProblemImpl* problem;
+  std::unique_ptr<ProblemImpl> gradient_checking_problem;
+  std::unique_ptr<Program> reduced_program;
+  std::unique_ptr<LinearSolver> linear_solver;
+  std::unique_ptr<IterationCallback> logging_callback;
+  std::unique_ptr<IterationCallback> state_updating_callback;
+
+  std::shared_ptr<Evaluator> evaluator;
+  std::shared_ptr<CoordinateDescentMinimizer> inner_iteration_minimizer;
+
+  std::vector<double*> removed_parameter_blocks;
+  Vector reduced_parameters;
+  double fixed_cost;
+};
+
+// Common functions used by various preprocessors.
+
+// If the user has specified a num_threads > the maximum number of threads
+// available from the compiled threading model, bound the number of threads
+// to the maximum.
+void ChangeNumThreadsIfNeeded(Solver::Options* options);
+
+// Extract the effective parameter vector from the preprocessed
+// problem and setup bits of the Minimizer::Options object that are
+// common to all Preprocessors.
+void SetupCommonMinimizerOptions(PreprocessedProblem* pp);
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_PREPROCESSOR_H_