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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2018 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: mierle@gmail.com (Keir Mierle)
+
+#ifndef CERES_PUBLIC_EVALUATION_CALLBACK_H_
+#define CERES_PUBLIC_EVALUATION_CALLBACK_H_
+
+#include "ceres/internal/port.h"
+
+namespace ceres {
+
+// Using this callback interface, Ceres can notify you when it is about to
+// evaluate the residuals or jacobians. With the callback, you can share
+// computation between residual blocks by doing the shared computation in
+// PrepareForEvaluation() before Ceres calls CostFunction::Evaluate() on all
+// the residuals. It also enables caching results between a pure residual
+// evaluation and a residual & jacobian evaluation, via the
+// new_evaluation_point argument.
+//
+// One use case for this callback is if the cost function compute is moved to
+// the GPU. In that case, the prepare call does the actual cost function
+// evaluation, and subsequent calls from Ceres to the actual cost functions
+// merely copy the results from the GPU onto the corresponding blocks for Ceres
+// to plug into the solver.
+//
+// NOTE: Ceres provides no mechanism to share data other than the notification
+// from the callback. Users must provide access to pre-computed shared data to
+// their cost functions behind the scenes; this all happens without Ceres
+// knowing. One approach is to put a pointer to the shared data in each cost
+// function (recommended) or to use a global shared variable (discouraged;
+// bug-prone). As far as Ceres is concerned, it is evaluating cost functions
+// like any other; it just so happens that behind the scenes the cost functions
+// reuse pre-computed data to execute faster.
+class CERES_EXPORT EvaluationCallback {
+ public:
+ virtual ~EvaluationCallback() {}
+
+ // Called before Ceres requests residuals or jacobians for a given setting of
+ // the parameters. User parameters (the double* values provided to the cost
+ // functions) are fixed until the next call to PrepareForEvaluation(). If
+ // new_evaluation_point == true, then this is a new point that is different
+ // from the last evaluated point. Otherwise, it is the same point that was
+ // evaluated previously (either jacobian or residual) and the user can use
+ // cached results from previous evaluations.
+ virtual void PrepareForEvaluation(bool evaluate_jacobians,
+ bool new_evaluation_point) = 0;
+};
+
+} // namespace ceres
+
+#endif // CERES_PUBLIC_EVALUATION_CALLBACK_H_