================================== General Unconstrained Minimization

While much of Ceres Solver is devoted to solving non-linear least squares problems, internally it contains a solver that can solve general unconstrained optimization problems using just their objective function value and gradients. The GradientProblem and GradientProblemSolver objects give the user access to this solver.

So without much further ado, let us look at how one goes about using them.

Rosenbrock's Function

We consider the minimization of the famous Rosenbrock's function <http://en.wikipedia.org/wiki/Rosenbrock_function>_ [#f1]_.

We begin by defining an instance of the FirstOrderFunction interface. This is the object that is responsible for computing the objective function value and the gradient (if required). This is the analog of the :class:CostFunction when defining non-linear least squares problems in Ceres.

.. code::

class Rosenbrock : public ceres::FirstOrderFunction { public: virtual bool Evaluate(const double* parameters, double* cost, double* gradient) const { const double x = parameters[0]; const double y = parameters[1];

  cost[0] = (1.0 - x) * (1.0 - x) + 100.0 * (y - x * x) * (y - x * x);
  if (gradient != NULL) {
    gradient[0] = -2.0 * (1.0 - x) - 200.0 * (y - x * x) * 2.0 * x;
    gradient[1] = 200.0 * (y - x * x);
  }
  return true;
}

virtual int NumParameters() const { return 2; }

};

Minimizing it then is a straightforward matter of constructing a :class:GradientProblem object and calling :func:Solve on it.

.. code::

double parameters[2] = {-1.2, 1.0};

ceres::GradientProblem problem(new Rosenbrock());

ceres::GradientProblemSolver::Options options;
options.minimizer_progress_to_stdout = true;
ceres::GradientProblemSolver::Summary summary;
ceres::Solve(options, problem, parameters, &summary);

std::cout << summary.FullReport() << "\n";

Executing this code results, solve the problem using limited memory BFGS <http://en.wikipedia.org/wiki/Broyden%E2%80%93Fletcher%E2%80%93Goldfarb%E2%80%93Shanno_algorithm>_ algorithm.

.. code-block:: bash

 0: f: 2.420000e+01 d: 0.00e+00 g: 2.16e+02 h: 0.00e+00 s: 0.00e+00 e:  0 it: 2.00e-05 tt: 2.00e-05
 1: f: 4.280493e+00 d: 1.99e+01 g: 1.52e+01 h: 2.01e-01 s: 8.62e-04 e:  2 it: 7.32e-05 tt: 2.19e-04
 2: f: 3.571154e+00 d: 7.09e-01 g: 1.35e+01 h: 3.78e-01 s: 1.34e-01 e:  3 it: 2.50e-05 tt: 2.68e-04
 3: f: 3.440869e+00 d: 1.30e-01 g: 1.73e+01 h: 1.36e-01 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 2.92e-04
 4: f: 3.213597e+00 d: 2.27e-01 g: 1.55e+01 h: 1.06e-01 s: 4.59e-01 e:  1 it: 2.86e-06 tt: 3.14e-04
 5: f: 2.839723e+00 d: 3.74e-01 g: 1.05e+01 h: 1.34e-01 s: 5.24e-01 e:  1 it: 2.86e-06 tt: 3.36e-04
 6: f: 2.448490e+00 d: 3.91e-01 g: 1.29e+01 h: 3.04e-01 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 3.58e-04
 7: f: 1.943019e+00 d: 5.05e-01 g: 4.00e+00 h: 8.81e-02 s: 7.43e-01 e:  1 it: 4.05e-06 tt: 3.79e-04
 8: f: 1.731469e+00 d: 2.12e-01 g: 7.36e+00 h: 1.71e-01 s: 4.60e-01 e:  2 it: 9.06e-06 tt: 4.06e-04
 9: f: 1.503267e+00 d: 2.28e-01 g: 6.47e+00 h: 8.66e-02 s: 1.00e+00 e:  1 it: 3.81e-06 tt: 4.33e-04
10: f: 1.228331e+00 d: 2.75e-01 g: 2.00e+00 h: 7.70e-02 s: 7.90e-01 e:  1 it: 3.81e-06 tt: 4.54e-04
11: f: 1.016523e+00 d: 2.12e-01 g: 5.15e+00 h: 1.39e-01 s: 3.76e-01 e:  2 it: 1.00e-05 tt: 4.82e-04
12: f: 9.145773e-01 d: 1.02e-01 g: 6.74e+00 h: 7.98e-02 s: 1.00e+00 e:  1 it: 3.10e-06 tt: 5.03e-04
13: f: 7.508302e-01 d: 1.64e-01 g: 3.88e+00 h: 5.76e-02 s: 4.93e-01 e:  1 it: 2.86e-06 tt: 5.25e-04
14: f: 5.832378e-01 d: 1.68e-01 g: 5.56e+00 h: 1.42e-01 s: 1.00e+00 e:  1 it: 3.81e-06 tt: 5.47e-04
15: f: 3.969581e-01 d: 1.86e-01 g: 1.64e+00 h: 1.17e-01 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 5.68e-04
16: f: 3.171557e-01 d: 7.98e-02 g: 3.84e+00 h: 1.18e-01 s: 3.97e-01 e:  2 it: 9.06e-06 tt: 5.94e-04
17: f: 2.641257e-01 d: 5.30e-02 g: 3.27e+00 h: 6.14e-02 s: 1.00e+00 e:  1 it: 3.10e-06 tt: 6.16e-04
18: f: 1.909730e-01 d: 7.32e-02 g: 5.29e-01 h: 8.55e-02 s: 6.82e-01 e:  1 it: 4.05e-06 tt: 6.42e-04
19: f: 1.472012e-01 d: 4.38e-02 g: 3.11e+00 h: 1.20e-01 s: 3.47e-01 e:  2 it: 1.00e-05 tt: 6.69e-04
20: f: 1.093558e-01 d: 3.78e-02 g: 2.97e+00 h: 8.43e-02 s: 1.00e+00 e:  1 it: 3.81e-06 tt: 6.91e-04
21: f: 6.710346e-02 d: 4.23e-02 g: 1.42e+00 h: 9.64e-02 s: 8.85e-01 e:  1 it: 3.81e-06 tt: 7.12e-04
22: f: 3.993377e-02 d: 2.72e-02 g: 2.30e+00 h: 1.29e-01 s: 4.63e-01 e:  2 it: 9.06e-06 tt: 7.39e-04
23: f: 2.911794e-02 d: 1.08e-02 g: 2.55e+00 h: 6.55e-02 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 7.62e-04
24: f: 1.457683e-02 d: 1.45e-02 g: 2.77e-01 h: 6.37e-02 s: 6.14e-01 e:  1 it: 3.81e-06 tt: 7.84e-04
25: f: 8.577515e-03 d: 6.00e-03 g: 2.86e+00 h: 1.40e-01 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 8.05e-04
26: f: 3.486574e-03 d: 5.09e-03 g: 1.76e-01 h: 1.23e-02 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 8.27e-04
27: f: 1.257570e-03 d: 2.23e-03 g: 1.39e-01 h: 5.08e-02 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 8.48e-04
28: f: 2.783568e-04 d: 9.79e-04 g: 6.20e-01 h: 6.47e-02 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 8.69e-04
29: f: 2.533399e-05 d: 2.53e-04 g: 1.68e-02 h: 1.98e-03 s: 1.00e+00 e:  1 it: 3.81e-06 tt: 8.91e-04
30: f: 7.591572e-07 d: 2.46e-05 g: 5.40e-03 h: 9.27e-03 s: 1.00e+00 e:  1 it: 3.81e-06 tt: 9.12e-04
31: f: 1.902460e-09 d: 7.57e-07 g: 1.62e-03 h: 1.89e-03 s: 1.00e+00 e:  1 it: 2.86e-06 tt: 9.33e-04
32: f: 1.003030e-12 d: 1.90e-09 g: 3.50e-05 h: 3.52e-05 s: 1.00e+00 e:  1 it: 3.10e-06 tt: 9.54e-04
33: f: 4.835994e-17 d: 1.00e-12 g: 1.05e-07 h: 1.13e-06 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 9.81e-04
34: f: 1.885250e-22 d: 4.84e-17 g: 2.69e-10 h: 1.45e-08 s: 1.00e+00 e:  1 it: 4.05e-06 tt: 1.00e-03

Solver Summary (v 1.12.0-lapack-suitesparse-cxsparse-no_openmp)

Parameters 2 Line search direction LBFGS (20) Line search type CUBIC WOLFE

Cost: Initial 2.420000e+01 Final 1.885250e-22 Change 2.420000e+01

Minimizer iterations 35

Time (in seconds):

Cost evaluation                       0.000
Gradient evaluation                   0.000

Total 0.003

Termination: CONVERGENCE (Gradient tolerance reached. Gradient max norm: 9.032775e-13 <= 1.000000e-10)

.. rubric:: Footnotes

.. [#f1] examples/rosenbrock.cc <https://ceres-solver.googlesource.com/ceres-solver/+/master/examples/rosenbrock.cc>_