internal/ceres/parameter_block.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2023 Google Inc. All rights reserved.
// http://ceres-solver.org/
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// Author: keir@google.com (Keir Mierle)

#ifndef CERES_INTERNAL_PARAMETER_BLOCK_H_
#define CERES_INTERNAL_PARAMETER_BLOCK_H_

#include <algorithm>
#include <cstdint>
#include <cstdlib>
#include <limits>
#include <memory>
#include <string>
#include <unordered_set>

#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/strings/str_format.h"
#include "ceres/array_utils.h"
#include "ceres/internal/disable_warnings.h"
#include "ceres/internal/eigen.h"
#include "ceres/internal/export.h"
#include "ceres/manifold.h"

namespace ceres::internal {

class ProblemImpl;
class ResidualBlock;

// The parameter block encodes the location of the user's original value, and
// also the "current state" of the parameter. The evaluator uses whatever is in
// the current state of the parameter when evaluating. This is inlined since the
// methods are performance sensitive.
//
// The class is not thread-safe, unless only const methods are called. The
// parameter block may also hold a pointer to a manifold; the parameter block
// does not take ownership of this pointer, so the user is responsible for the
// proper disposal of the manifold.
class CERES_NO_EXPORT ParameterBlock {
 public:
  using ResidualBlockSet = std::unordered_set<ResidualBlock*>;

  // Create a parameter block with the user state, size, and index specified.
  // The size is the size of the parameter block and the index is the position
  // of the parameter block inside a Program (if any).
  ParameterBlock(double* user_state, int size, int index)
      : user_state_(user_state),
        size_(size),
        state_(user_state),
        index_(index) {}

  ParameterBlock(double* user_state, int size, int index, Manifold* manifold)
      : user_state_(user_state),
        size_(size),
        state_(user_state),
        index_(index) {
    if (manifold != nullptr) {
      SetManifold(manifold);
    }
  }

  // The size of the parameter block.
  int Size() const { return size_; }

  // Manipulate the parameter state.
  bool SetState(const double* x) {
    CHECK(x != nullptr) << "Tried to set the state of constant parameter "
                        << "with user location " << user_state_;
    CHECK(!IsConstant()) << "Tried to set the state of constant parameter "
                         << "with user location " << user_state_;

    state_ = x;
    return UpdatePlusJacobian();
  }

  // Copy the current parameter state out to x. This is "GetState()" rather than
  // simply "state()" since it is actively copying the data into the passed
  // pointer.
  void GetState(double* x) const {
    if (x != state_) {
      std::copy(state_, state_ + size_, x);
    }
  }

  // Direct pointers to the current state.
  const double* state() const { return state_; }
  const double* user_state() const { return user_state_; }
  double* mutable_user_state() { return user_state_; }
  const Manifold* manifold() const { return manifold_; }
  Manifold* mutable_manifold() { return manifold_; }

  // Set this parameter block to vary or not.
  void SetConstant() { is_set_constant_ = true; }
  void SetVarying() { is_set_constant_ = false; }
  bool IsConstant() const { return (is_set_constant_ || TangentSize() == 0); }

  double UpperBound(int index) const {
    return (upper_bounds_ ? upper_bounds_[index]
                          : std::numeric_limits<double>::max());
  }

  double LowerBound(int index) const {
    return (lower_bounds_ ? lower_bounds_[index]
                          : -std::numeric_limits<double>::max());
  }

  bool IsUpperBounded() const { return (upper_bounds_ == nullptr); }
  bool IsLowerBounded() const { return (lower_bounds_ == nullptr); }

  // This parameter block's index in an array.
  int index() const { return index_; }
  void set_index(int index) { index_ = index; }

  // This parameter offset inside a larger state vector.
  int state_offset() const { return state_offset_; }
  void set_state_offset(int state_offset) { state_offset_ = state_offset; }

  // This parameter offset inside a larger delta vector.
  int delta_offset() const { return delta_offset_; }
  void set_delta_offset(int delta_offset) { delta_offset_ = delta_offset; }

  // Methods relating to the parameter block's manifold.

  // The local to global jacobian. Returns nullptr if there is no manifold for
  // this parameter block. The returned matrix is row-major and has Size() rows
  // and TangentSize() columns.
  const double* PlusJacobian() const { return plus_jacobian_.get(); }

  int TangentSize() const {
    return (manifold_ == nullptr) ? size_ : manifold_->TangentSize();
  }

  // Set the manifold. The parameter block does not take ownership of
  // the manifold.
  void SetManifold(Manifold* new_manifold) {
    // Nothing to do if the new manifold is the same as the old
    // manifold.
    if (new_manifold == manifold_) {
      return;
    }

    if (new_manifold == nullptr) {
      manifold_ = nullptr;
      plus_jacobian_ = nullptr;
      return;
    }

    CHECK_EQ(new_manifold->AmbientSize(), size_)
        << "The parameter block has size = " << size_
        << " while the manifold has ambient size = "
        << new_manifold->AmbientSize();

    CHECK_GE(new_manifold->TangentSize(), 0)
        << "Invalid Manifold. Manifolds must have a "
        << "non-negative dimensional tangent space.";

    manifold_ = new_manifold;
    plus_jacobian_ = std::make_unique<double[]>(manifold_->AmbientSize() *
                                                manifold_->TangentSize());
    CHECK(UpdatePlusJacobian())
        << "Manifold::PlusJacobian computation failed for x: "
        << ConstVectorRef(state_, Size()).transpose();
  }

  void SetUpperBound(int index, double upper_bound) {
    CHECK_LT(index, size_);

    if (upper_bound >= std::numeric_limits<double>::max() && !upper_bounds_) {
      return;
    }

    if (!upper_bounds_) {
      upper_bounds_ = std::make_unique<double[]>(size_);
      std::fill(upper_bounds_.get(),
                upper_bounds_.get() + size_,
                std::numeric_limits<double>::max());
    }

    upper_bounds_[index] = upper_bound;
  }

  void SetLowerBound(int index, double lower_bound) {
    CHECK_LT(index, size_);

    if (lower_bound <= -std::numeric_limits<double>::max() && !lower_bounds_) {
      return;
    }

    if (!lower_bounds_) {
      lower_bounds_ = std::make_unique<double[]>(size_);
      std::fill(lower_bounds_.get(),
                lower_bounds_.get() + size_,
                -std::numeric_limits<double>::max());
    }

    lower_bounds_[index] = lower_bound;
  }

  // Generalization of the addition operation. This is the same as
  // Manifold::Plus() followed by projection onto the
  // hyper cube implied by the bounds constraints.
  bool Plus(const double* x, const double* delta, double* x_plus_delta) {
    if (manifold_ != nullptr) {
      if (!manifold_->Plus(x, delta, x_plus_delta)) {
        return false;
      }
    } else {
      VectorRef(x_plus_delta, size_) =
          ConstVectorRef(x, size_) + ConstVectorRef(delta, size_);
    }

    // Project onto the box constraints.
    if (lower_bounds_.get() != nullptr) {
      for (int i = 0; i < size_; ++i) {
        x_plus_delta[i] = std::max(x_plus_delta[i], lower_bounds_[i]);
      }
    }

    if (upper_bounds_.get() != nullptr) {
      for (int i = 0; i < size_; ++i) {
        x_plus_delta[i] = std::min(x_plus_delta[i], upper_bounds_[i]);
      }
    }

    return true;
  }

  std::string ToString() const {
    return absl::StrFormat(
        "{ this=%p, user_state=%p, state=%p, size=%d, "
        "constant=%d, index=%d, state_offset=%d, "
        "delta_offset=%d }",
        this,
        user_state_,
        state_,
        size_,
        is_set_constant_,
        index_,
        state_offset_,
        delta_offset_);
  }

  void EnableResidualBlockDependencies() {
    CHECK(residual_blocks_.get() == nullptr)
        << "Ceres bug: There is already a residual block collection "
        << "for parameter block: " << ToString();
    residual_blocks_ = std::make_unique<ResidualBlockSet>();
  }

  void AddResidualBlock(ResidualBlock* residual_block) {
    CHECK(residual_blocks_.get() != nullptr)
        << "Ceres bug: The residual block collection is null for parameter "
        << "block: " << ToString();
    residual_blocks_->insert(residual_block);
  }

  void RemoveResidualBlock(ResidualBlock* residual_block) {
    CHECK(residual_blocks_.get() != nullptr)
        << "Ceres bug: The residual block collection is null for parameter "
        << "block: " << ToString();
    CHECK(residual_blocks_->find(residual_block) != residual_blocks_->end())
        << "Ceres bug: Missing residual for parameter block: " << ToString();
    residual_blocks_->erase(residual_block);
  }

  // This is only intended for iterating; perhaps this should only expose
  // .begin() and .end().
  ResidualBlockSet* mutable_residual_blocks() { return residual_blocks_.get(); }

  double LowerBoundForParameter(int index) const {
    if (lower_bounds_.get() == nullptr) {
      return -std::numeric_limits<double>::max();
    } else {
      return lower_bounds_[index];
    }
  }

  double UpperBoundForParameter(int index) const {
    if (upper_bounds_.get() == nullptr) {
      return std::numeric_limits<double>::max();
    } else {
      return upper_bounds_[index];
    }
  }

 private:
  bool UpdatePlusJacobian() {
    if (manifold_ == nullptr) {
      return true;
    }

    // Update the Plus Jacobian. In some cases this is
    // wasted effort; if this is a bottleneck, we will find a solution
    // at that time.
    const int jacobian_size = Size() * TangentSize();
    InvalidateArray(jacobian_size, plus_jacobian_.get());
    if (!manifold_->PlusJacobian(state_, plus_jacobian_.get())) {
      LOG(WARNING) << "Manifold::PlusJacobian computation failed"
                      "for x: "
                   << ConstVectorRef(state_, Size()).transpose();
      return false;
    }

    if (!IsArrayValid(jacobian_size, plus_jacobian_.get())) {
      LOG(WARNING) << "Manifold::PlusJacobian computation returned "
                   << "an invalid matrix for x: "
                   << ConstVectorRef(state_, Size()).transpose()
                   << "\n Jacobian matrix : "
                   << ConstMatrixRef(
                          plus_jacobian_.get(), Size(), TangentSize());
      return false;
    }
    return true;
  }

  double* user_state_ = nullptr;
  int size_ = -1;
  bool is_set_constant_ = false;
  Manifold* manifold_ = nullptr;

  // The "state" of the parameter. These fields are only needed while the
  // solver is running. While at first glance using mutable is a bad idea, this
  // ends up simplifying the internals of Ceres enough to justify the potential
  // pitfalls of using "mutable."
  mutable const double* state_ = nullptr;
  mutable std::unique_ptr<double[]> plus_jacobian_;

  // The index of the parameter. This is used by various other parts of Ceres to
  // permit switching from a ParameterBlock* to an index in another array.
  int index_ = -1;

  // The offset of this parameter block inside a larger state vector.
  int state_offset_ = -1;

  // The offset of this parameter block inside a larger delta vector.
  int delta_offset_ = -1;

  // If non-null, contains the residual blocks this parameter block is in.
  std::unique_ptr<ResidualBlockSet> residual_blocks_;

  // Upper and lower bounds for the parameter block.  SetUpperBound
  // and SetLowerBound lazily initialize the upper_bounds_ and
  // lower_bounds_ arrays. If they are never called, then memory for
  // these arrays is never allocated. Thus for problems where there
  // are no bounds, or only one sided bounds we do not pay the cost of
  // allocating memory for the inactive bounds constraints.
  //
  // Upon initialization these arrays are initialized to
  // std::numeric_limits<double>::max() and
  // -std::numeric_limits<double>::max() respectively which correspond
  // to the parameter block being unconstrained.
  std::unique_ptr<double[]> upper_bounds_;
  std::unique_ptr<double[]> lower_bounds_;

  // Necessary so ProblemImpl can clean up the manifolds.
  friend class ProblemImpl;
};

}  // namespace ceres::internal

#include "ceres/internal/reenable_warnings.h"

#endif  // CERES_INTERNAL_PARAMETER_BLOCK_H_