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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 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: strandmark@google.com (Petter Strandmark)
+//
+// Class for loading the data required for descibing a Fields of Experts (FoE)
+// model. The Fields of Experts regularization consists of terms of the type
+//
+//   alpha * log(1 + (1/2)*sum(F .* X)^2),
+//
+// where F is a d-by-d image patch and alpha is a constant. This is implemented
+// by a FieldsOfExpertsSum object which represents the dot product between the
+// image patches and a FieldsOfExpertsLoss which implements the log(1 + (1/2)s)
+// part.
+//
+// [1] S. Roth and M.J. Black. "Fields of Experts." International Journal of
+//     Computer Vision, 82(2):205--229, 2009.
+
+#ifndef CERES_EXAMPLES_FIELDS_OF_EXPERTS_H_
+#define CERES_EXAMPLES_FIELDS_OF_EXPERTS_H_
+
+#include <iostream>
+#include <vector>
+
+#include "ceres/loss_function.h"
+#include "ceres/cost_function.h"
+#include "ceres/sized_cost_function.h"
+
+#include "pgm_image.h"
+
+namespace ceres {
+namespace examples {
+
+// One sum in the FoE regularizer. This is a dot product between a filter and an
+// image patch. It simply calculates the dot product between the filter
+// coefficients given in the constructor and the scalar parameters passed to it.
+class FieldsOfExpertsCost : public ceres::CostFunction {
+ public:
+  explicit FieldsOfExpertsCost(const std::vector<double>& filter);
+  // The number of scalar parameters passed to Evaluate must equal the number of
+  // filter coefficients passed to the constructor.
+  virtual bool Evaluate(double const* const* parameters,
+                        double* residuals,
+                        double** jacobians) const;
+
+ private:
+  const std::vector<double>& filter_;
+};
+
+// The loss function used to build the correct regularization. See above.
+//
+//   f(x) = alpha_i * log(1 + (1/2)s)
+//
+class FieldsOfExpertsLoss : public ceres::LossFunction {
+ public:
+  explicit FieldsOfExpertsLoss(double alpha) : alpha_(alpha) { }
+  virtual void Evaluate(double, double*) const;
+
+ private:
+  const double alpha_;
+};
+
+// This class loads a set of filters and coefficients from file. Then the users
+// obtains the correct loss and cost functions through NewCostFunction and
+// NewLossFunction.
+class FieldsOfExperts {
+ public:
+  // Creates an empty object with size() == 0.
+  FieldsOfExperts();
+  // Attempts to load filters from a file. If unsuccessful it returns false and
+  // sets size() == 0.
+  bool LoadFromFile(const std::string& filename);
+
+  // Side length of a square filter in this FoE. They are all of the same size.
+  int Size() const {
+    return size_;
+  }
+
+  // Total number of pixels the filter covers.
+  int NumVariables() const {
+    return size_ * size_;
+  }
+
+  // Number of filters used by the FoE.
+  int NumFilters() const {
+    return num_filters_;
+  }
+
+  // Creates a new cost function. The caller is responsible for deallocating the
+  // memory. alpha_index specifies which filter is used in the cost function.
+  ceres::CostFunction* NewCostFunction(int alpha_index) const;
+  // Creates a new loss function. The caller is responsible for deallocating the
+  // memory. alpha_index specifies which filter this loss function is for.
+  ceres::LossFunction* NewLossFunction(int alpha_index) const;
+
+  // Gets the delta pixel indices for all pixels in a patch.
+  const std::vector<int>& GetXDeltaIndices() const {
+    return x_delta_indices_;
+  }
+  const std::vector<int>& GetYDeltaIndices() const {
+    return y_delta_indices_;
+  }
+
+ private:
+  // The side length of a square filter.
+  int size_;
+  // The number of different filters used.
+  int num_filters_;
+  // Pixel offsets for all variables.
+  std::vector<int> x_delta_indices_, y_delta_indices_;
+  // The coefficients in front of each term.
+  std::vector<double> alpha_;
+  // The filters used for the dot product with image patches.
+  std::vector<std::vector<double> > filters_;
+};
+
+}  // namespace examples
+}  // namespace ceres
+
+#endif  // CERES_EXAMPLES_FIELDS_OF_EXPERTS_H_