1 // Ceres Solver - A fast non-linear least squares minimizer
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3 // http://ceres-solver.org/
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29 // Author: sameeragarwal@google.com (Sameer Agarwal)
31 // Create CostFunctions as needed by the least squares framework, with
32 // Jacobians computed via automatic differentiation. For more
33 // information on automatic differentation, see the wikipedia article
34 // at http://en.wikipedia.org/wiki/Automatic_differentiation
36 // To get an auto differentiated cost function, you must define a class with a
37 // templated operator() (a functor) that computes the cost function in terms of
38 // the template parameter T. The autodiff framework substitutes appropriate
39 // "jet" objects for T in order to compute the derivative when necessary, but
40 // this is hidden, and you should write the function as if T were a scalar type
41 // (e.g. a double-precision floating point number).
43 // The function must write the computed value in the last argument
44 // (the only non-const one) and return true to indicate
45 // success. Please see cost_function.h for details on how the return
46 // value maybe used to impose simple constraints on the parameter
49 // For example, consider a scalar error e = k - x'y, where both x and y are
50 // two-dimensional column vector parameters, the prime sign indicates
51 // transposition, and k is a constant. The form of this error, which is the
52 // difference between a constant and an expression, is a common pattern in least
53 // squares problems. For example, the value x'y might be the model expectation
54 // for a series of measurements, where there is an instance of the cost function
55 // for each measurement k.
57 // The actual cost added to the total problem is e^2, or (k - x'k)^2; however,
58 // the squaring is implicitly done by the optimization framework.
60 // To write an auto-differentiable cost function for the above model, first
63 // class MyScalarCostFunctor {
64 // MyScalarCostFunctor(double k): k_(k) {}
66 // template <typename T>
67 // bool operator()(const T* const x , const T* const y, T* e) const {
68 // e[0] = T(k_) - x[0] * y[0] + x[1] * y[1];
76 // Note that in the declaration of operator() the input parameters x and y come
77 // first, and are passed as const pointers to arrays of T. If there were three
78 // input parameters, then the third input parameter would come after y. The
79 // output is always the last parameter, and is also a pointer to an array. In
80 // the example above, e is a scalar, so only e[0] is set.
82 // Then given this class definition, the auto differentiated cost function for
83 // it can be constructed as follows.
85 // CostFunction* cost_function
86 // = new AutoDiffCostFunction<MyScalarCostFunctor, 1, 2, 2>(
87 // new MyScalarCostFunctor(1.0)); ^ ^ ^
89 // Dimension of residual -----+ | |
90 // Dimension of x ---------------+ |
91 // Dimension of y ------------------+
93 // In this example, there is usually an instance for each measumerent of k.
95 // In the instantiation above, the template parameters following
96 // "MyScalarCostFunctor", "1, 2, 2", describe the functor as computing a
97 // 1-dimensional output from two arguments, both 2-dimensional.
99 // AutoDiffCostFunction also supports cost functions with a
100 // runtime-determined number of residuals. For example:
102 // CostFunction* cost_function
103 // = new AutoDiffCostFunction<MyScalarCostFunctor, DYNAMIC, 2, 2>(
104 // new CostFunctorWithDynamicNumResiduals(1.0), ^ ^ ^
105 // runtime_number_of_residuals); <----+ | | |
108 // Actual number of residuals ------+ | | |
109 // Indicate dynamic number of residuals --------+ | |
110 // Dimension of x ------------------------------------+ |
111 // Dimension of y ---------------------------------------+
113 // The framework can currently accommodate cost functions of up to 10
114 // independent variables, and there is no limit on the dimensionality
117 // WARNING #1: Since the functor will get instantiated with different types for
118 // T, you must to convert from other numeric types to T before mixing
119 // computations with other variables of type T. In the example above, this is
120 // seen where instead of using k_ directly, k_ is wrapped with T(k_).
122 // WARNING #2: A common beginner's error when first using autodiff cost
123 // functions is to get the sizing wrong. In particular, there is a tendency to
124 // set the template parameters to (dimension of residual, number of parameters)
125 // instead of passing a dimension parameter for *every parameter*. In the
126 // example above, that would be <MyScalarCostFunctor, 1, 2>, which is missing
127 // the last '2' argument. Please be careful when setting the size parameters.
129 #ifndef CERES_PUBLIC_AUTODIFF_COST_FUNCTION_H_
130 #define CERES_PUBLIC_AUTODIFF_COST_FUNCTION_H_
132 #include "ceres/internal/autodiff.h"
133 #include "ceres/internal/scoped_ptr.h"
134 #include "ceres/sized_cost_function.h"
135 #include "ceres/types.h"
136 #include "glog/logging.h"
140 // A cost function which computes the derivative of the cost with respect to
141 // the parameters (a.k.a. the jacobian) using an autodifferentiation framework.
142 // The first template argument is the functor object, described in the header
143 // comment. The second argument is the dimension of the residual (or
144 // ceres::DYNAMIC to indicate it will be set at runtime), and subsequent
145 // arguments describe the size of the Nth parameter, one per parameter.
147 // The constructors take ownership of the cost functor.
149 // If the number of residuals (argument kNumResiduals below) is
150 // ceres::DYNAMIC, then the two-argument constructor must be used. The
151 // second constructor takes a number of residuals (in addition to the
152 // templated number of residuals). This allows for varying the number
153 // of residuals for a single autodiff cost function at runtime.
154 template <typename CostFunctor,
155 int kNumResiduals, // Number of residuals, or ceres::DYNAMIC.
156 int N0, // Number of parameters in block 0.
157 int N1 = 0, // Number of parameters in block 1.
158 int N2 = 0, // Number of parameters in block 2.
159 int N3 = 0, // Number of parameters in block 3.
160 int N4 = 0, // Number of parameters in block 4.
161 int N5 = 0, // Number of parameters in block 5.
162 int N6 = 0, // Number of parameters in block 6.
163 int N7 = 0, // Number of parameters in block 7.
164 int N8 = 0, // Number of parameters in block 8.
165 int N9 = 0> // Number of parameters in block 9.
166 class AutoDiffCostFunction : public SizedCostFunction<kNumResiduals,
168 N5, N6, N7, N8, N9> {
170 // Takes ownership of functor. Uses the template-provided value for the
171 // number of residuals ("kNumResiduals").
172 explicit AutoDiffCostFunction(CostFunctor* functor)
173 : functor_(functor) {
174 CHECK_NE(kNumResiduals, DYNAMIC)
175 << "Can't run the fixed-size constructor if the "
176 << "number of residuals is set to ceres::DYNAMIC.";
179 // Takes ownership of functor. Ignores the template-provided
180 // kNumResiduals in favor of the "num_residuals" argument provided.
182 // This allows for having autodiff cost functions which return varying
183 // numbers of residuals at runtime.
184 AutoDiffCostFunction(CostFunctor* functor, int num_residuals)
185 : functor_(functor) {
186 CHECK_EQ(kNumResiduals, DYNAMIC)
187 << "Can't run the dynamic-size constructor if the "
188 << "number of residuals is not ceres::DYNAMIC.";
189 SizedCostFunction<kNumResiduals,
192 ::set_num_residuals(num_residuals);
195 virtual ~AutoDiffCostFunction() {}
197 // Implementation details follow; clients of the autodiff cost function should
198 // not have to examine below here.
200 // To handle varardic cost functions, some template magic is needed. It's
201 // mostly hidden inside autodiff.h.
202 virtual bool Evaluate(double const* const* parameters,
204 double** jacobians) const {
206 return internal::VariadicEvaluate<
207 CostFunctor, double, N0, N1, N2, N3, N4, N5, N6, N7, N8, N9>
208 ::Call(*functor_, parameters, residuals);
210 return internal::AutoDiff<CostFunctor, double,
211 N0, N1, N2, N3, N4, N5, N6, N7, N8, N9>::Differentiate(
214 SizedCostFunction<kNumResiduals,
216 N5, N6, N7, N8, N9>::num_residuals(),
222 internal::scoped_ptr<CostFunctor> functor_;
227 #endif // CERES_PUBLIC_AUTODIFF_COST_FUNCTION_H_