env/ceres-solver/include/ceres/sized_cost_function.h

// Ceres Solver - A fast non-linear least squares minimizer
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// Author: keir@google.com (Keir Mierle)
//
// A convenience class for cost functions which are statically sized.
// Compared to the dynamically-sized base class, this reduces boilerplate.
//
// The kNumResiduals template parameter can be a constant such as 2 or 5, or it
// can be ceres::DYNAMIC. If kNumResiduals is ceres::DYNAMIC, then subclasses
// are responsible for calling set_num_residuals() at runtime.

#ifndef CERES_PUBLIC_SIZED_COST_FUNCTION_H_
#define CERES_PUBLIC_SIZED_COST_FUNCTION_H_

#include "ceres/cost_function.h"
#include "ceres/types.h"
#include "glog/logging.h"
#include "internal/parameter_dims.h"

namespace ceres {

template <int kNumResiduals, int... Ns>
class SizedCostFunction : public CostFunction {
 public:
  static_assert(kNumResiduals > 0 || kNumResiduals == DYNAMIC,
                "Cost functions must have at least one residual block.");
  static_assert(internal::StaticParameterDims<Ns...>::kIsValid,
                "Invalid parameter block dimension detected. Each parameter "
                "block dimension must be bigger than zero.");

  using ParameterDims = internal::StaticParameterDims<Ns...>;

  SizedCostFunction() {
    set_num_residuals(kNumResiduals);
    *mutable_parameter_block_sizes() = std::vector<int32_t>{Ns...};
  }

  // Subclasses must implement Evaluate().
};

}  // namespace ceres

#endif  // CERES_PUBLIC_SIZED_COST_FUNCTION_H_