Added a bunch of unconstrained optimization stuff to the library.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402264

dlib/algs.h

@@ -495,6 +495,46 @@ namespace dlib
     template <typename T> inline typename disable_if<is_built_in_scalar_type<T>,void>::type assign_zero_if_built_in_scalar_type (T&){}
     template <typename T> inline typename enable_if<is_built_in_scalar_type<T>,void>::type assign_zero_if_built_in_scalar_type (T& a){a=0;}
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    T put_in_range (
+        const T& a, 
+        const T& b, 
+        const T& val
+    )
+    /*!
+        requires
+            - T is a type that looks like double, float, int, or so forth
+        ensures
+            - if (val is within the range [a,b]) then
+                - returns val
+            - else 
+                - returns the end of the range [a,b] that is closest to val
+    !*/
+    {
+        if (a < b)
+        {
+            if (val < a)
+                return a;
+            else if (val > b)
+                return b;
+        }
+        else
+        {
+            if (val < b)
+                return b;
+            else if (val > a)
+                return a;
+        }
+
+        return val;
+    }
+
+    // overload for double 
+    inline double put_in_range(const double& a, const double& b, const double& val)
+    { return put_in_range<double>(a,b,val); }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/optimization.h

+// Copyright (C) 2008  Davis E. King (davisking@users.sourceforge.net)
+// License: Boost Software License   See LICENSE.txt for the full license.
+#ifndef DLIB_OPTIMIZATIOn_HEADER
+#define DLIB_SVM_HEADER
+
+#include "optimization/optimization.h"
+
+#endif // DLIB_OPTIMIZATIOn_HEADER
+
+
+

dlib/optimization/optimization.h

+// Copyright (C) 2008  Davis E. King (davisking@users.sourceforge.net)
+// License: Boost Software License   See LICENSE.txt for the full license.
+#ifndef DLIB_OPTIMIZATIOn_H_
+#define DLIB_OPTIMIZATIOn_H_
+
+#include <cmath>
+#include <limits>
+#include "../matrix.h"
+#include "../algs.h"
+#include "optimization_abstract.h"
+
+namespace dlib
+{
+
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+//                    Functions that transform other functions  
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+
+    template <typename funct>
+    class central_differences
+    {
+    public:
+        central_differences(const funct& f_, double eps_ = 1e-7) : f(f_), eps(eps_){}
+
+        template <typename T>
+        typename T::matrix_type operator()(const T& x) const
+        {
+            // T must be some sort of dlib matrix 
+            COMPILE_TIME_ASSERT(is_matrix<T>::value);
+
+            typename T::matrix_type der(x.size());
+            typename T::matrix_type e(x.size());
+            set_all_elements(e,0);
+            for (long i = 0; i < x.size(); ++i)
+            {
+                e(i) = 1;
+                der(i) = (f(x+e*eps)-f(x-e*eps))/(2*eps);
+                e(i) = 0;
+            }
+
+            return der;
+        }
+
+        double operator()(const double& x) const
+        {
+            return (f(x+eps)-f(x-eps))/(2*eps);
+        }
+
+    private:
+        const funct& f;
+        const double eps;
+    };
+
+    template <typename funct>
+    const central_differences<funct> derivative(const funct& f) { return central_differences<funct>(f); }
+    template <typename funct>
+    const central_differences<funct> derivative(const funct& f, double eps) { return central_differences<funct>(f,eps); }
+
+// ----------------------------------------------------------------------------------------
+
+    template <typename funct, typename T>
+    class line_search_funct 
+    {
+    public:
+        line_search_funct(const funct& f_, const T& start_, const T& direction_) : f(f_),start(start_), direction(direction_)
+        {}
+
+        double operator()(const double& x) const
+        {
+            return get_value(f(start + x*direction));
+        }
+
+    private:
+
+        double get_value (const double& r) const
+        {
+            return r;
+        }
+
+        template <typename U>
+        double get_value (const U& r) const
+        {
+            // U should be a matrix type
+            COMPILE_TIME_ASSERT(is_matrix<U>::value);
+
+            return trans(r)*direction;
+        }
+
+        const funct& f;
+        const T& start;
+        const T& direction;
+    };
+
+    template <typename funct, typename T>
+    const line_search_funct<funct,T> make_line_search_function(const funct& f, const T& start, const T& direction) 
+    { 
+        COMPILE_TIME_ASSERT(is_matrix<T>::value);
+        DLIB_ASSERT (
+            start.nc() == 1 && direction.nc() == 1,
+            "\tline_search_funct make_line_search_function(f,start,direction)"
+            << "\n\tYou have to supply column vectors to this function"
+            << "\n\tstart.nc():     " << start.nc()
+            << "\n\tdirection.nc(): " << direction.nc()
+        );
+        return line_search_funct<funct,T>(f,start,direction); 
+    }
+
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+//                    Functions that perform unconstrained optimization 
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+
+    inline double poly_min_extrap (
+        double f0,
+        double d0,
+        double f1,
+        double d1
+    )
+    {
+        const double n = 3*(f1 - f0) - 2*d0 - d1;
+        const double e = d0 + d1 - 2*(f1 - f0);
+
+
+        // find the minimum of the derivative of the polynomial
+
+        double temp = std::max(n*n - 3*e*d0,0.0);
+
+        if (temp < 0)
+            return 0.5;
+
+        temp = std::sqrt(temp);
+
+        if (std::abs(e) <= std::numeric_limits<double>::epsilon())
+            return 0.5;
+
+        // figure out the two possible min values
+        double x1 = (temp - n)/(3*e);
+        double x2 = -(temp + n)/(3*e);
+
+        // compute the value of the interpolating polynomial at these two points
+        double y1 = f0 + d0*x1 + n*x1*x1 + e*x1*x1*x1;
+        double y2 = f0 + d0*x2 + n*x2*x2 + e*x2*x2*x2;
+
+        // pick the best point
+        double x;
+        if (y1 < y2)
+            x = x1;
+        else
+            x = x2;
+
+        // now make sure the minimum is within the allowed range of (0,1) 
+        return put_in_range(0,1,x);
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename funct_der
+        >
+    double line_search (
+        const funct& f, 
+        const funct_der& der, 
+        double rho, 
+        double sigma, 
+        double minf,
+        double& f0_out
+    )
+    {
+        DLIB_ASSERT (
+            1 > sigma && sigma > rho && rho > 0,
+            "\tdouble line_search()"
+            << "\n\tYou have given invalid arguments to this function"
+            << "\n\tsigma: " << sigma
+            << "\n\trho:   " << rho 
+        );
+
+        // The bracketing phase of this function is implemented according to block 2.6.2 from
+        // the book Practical Methods of Optimization by R. Fletcher.   The sectioning 
+        // phase is an implementation of 2.6.4 from the same book.
+
+        // tau1 > 1. Controls the alpha jump size during the search
+        const double tau1 = 9;
+
+        // it must be the case that 0 < tau2 < tau3 <= 1/2 for the algorithm to function
+        // correctly but the specific values of tau2 and tau3 aren't super important.
+        const double tau2 = 1.0/10.0;
+        const double tau3 = 1.0/2.0;
+
+        const double f0 = f(0);
+        const double d0 = der(0);
+
+        if (std::abs(d0) < std::numeric_limits<double>::epsilon())
+            return 0;
+        //DLIB_CASSERT(d0 < 0,d0);
+
+        const double mu = (minf-f0)/(rho*d0);
+
+
+        f0_out = f0;
+
+
+        double f1 = f(mu);
+        double d1 = der(mu);
+        // pick the initial alpha by guessing at the minimum alpha 
+        double alpha = mu*poly_min_extrap(f0, d0, f1, d1);
+        alpha = put_in_range(0.1*mu, 0.9*mu, alpha);
+
+        DLIB_CASSERT(alpha < std::numeric_limits<double>::infinity(), alpha);
+
+        double last_alpha = 0;
+        double last_val = f0;
+        double last_val_der = d0;
+
+        // the bracketing stage will find a find a range of points [a,b]
+        // that contains a reasonable solution to the line search
+        double a, b;
+
+        // the value of f(a)
+        double a_val, b_val, a_val_der, b_val_der;
+
+        const double thresh = std::abs(sigma*d0);
+
+        // do the bracketing stage to find the bracket range [a,b]
+        while (true)
+        {
+            DLIB_CASSERT(alpha < std::numeric_limits<double>::infinity(), alpha);
+            const double val = f(alpha);
+            const double val_der = der(alpha);
+
+            // we are done with the line search since we found a value smaller
+            // than the minimum f value
+            if (val <= minf)
+                return alpha;
+
+            if (val > f0 + alpha*d0 || val >= last_val)
+            {
+                a_val = last_val;
+                a_val_der = last_val_der;
+                b_val = val;
+                b_val_der = val_der;
+
+                a = last_alpha;
+                b = alpha;
+                break;
+            }
+
+            if (std::abs(val_der) <= thresh)
+                return alpha;
+
+            // if we are stuck not making progress then quit with the current alpha
+            if (last_alpha == alpha)
+                return alpha;
+
+            if (val_der >= 0)
+            {
+                a_val = val;
+                a_val_der = val_der;
+                b_val = last_val;
+                b_val_der = last_val_der;
+
+                a = alpha;
+                b = last_alpha;
+                break;
+            }
+
+            if (mu <= 2*alpha - last_alpha)
+            {
+                last_alpha = alpha;
+                alpha = mu;
+            }
+            else
+            {
+                const double temp = alpha;
+
+                double first = 2*alpha - last_alpha;
+                double last;
+                if (mu > 0)
+                    last = std::min(mu, alpha + tau1*(alpha - last_alpha));
+                else
+                    last = std::max(mu, alpha + tau1*(alpha - last_alpha));
+
+
+                // pick a point between first and last by doing some kind of interpolation
+                if (last_alpha < alpha)
+                    alpha = last_alpha + (alpha-last_alpha)*poly_min_extrap(last_val, last_val_der, val, val_der);
+                else
+                    alpha = alpha + (last_alpha-alpha)*poly_min_extrap(val, val_der, last_val, last_val_der);
+
+                alpha = put_in_range(first,last,alpha);
+
+                alpha = (first+last)/2;
+
+                last_alpha = temp;
+            }
+
+            last_val = val;
+            last_val_der = val_der;
+
+        }
+
+
+        DLIB_CASSERT(alpha < std::numeric_limits<double>::infinity(), alpha);
+
+        // Now do the sectioning phase from 2.6.4
+        while (true)
+        {
+            DLIB_CASSERT(alpha < std::numeric_limits<double>::infinity(), alpha);
+            double first = a + tau2*(b-a);
+            double last = b - tau3*(b-a);
+
+            // use interpolation to pick alpha between first and last
+            alpha = a + (b-a)*poly_min_extrap(a_val, a_val_der, b_val, b_val_der);
+            alpha = put_in_range(first,last,alpha);
+            //alpha = (first+last)/2;
+
+            const double val = f(alpha);
+            const double val_der = der(alpha);
+
+
+            // stop if the interval gets so small that it isn't shrinking any more due to rounding error 
+            if (a == first || b == last)
+            {
+                return b;
+            }
+
+
+            if (val > f0 + rho*alpha*d0 || val >= a_val)
+            {
+                b = alpha;
+                b_val = val;
+                b_val_der = val_der;
+            }
+            else
+            {
+                if (std::abs(val_der) <= thresh)
+                    return alpha;
+
+                if ( (b-a)*val_der >= 0)
+                {
+                    b = a;
+                    b_val = a_val;
+                    b_val_der = a_val_der;
+                }
+
+                a = alpha;
+                a_val = val;
+                a_val_der = val_der;
+            }
+        }
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename funct_der, 
+        typename T
+        >
+    double quasi_newton (
+        const funct& f, 
+        const funct_der& der, 
+        T& x, 
+        double min_f,
+        double min_delta = 1e-7 
+    )
+    {
+        COMPILE_TIME_ASSERT(is_matrix<T>::value);
+        DLIB_ASSERT (
+            min_delta >= 0 && x.nc() == 1,
+            "\tdouble quasi_newton()"
+            << "\n\tYou have to supply column vectors to this function"
+            << "\n\tmin_delta: " << min_delta
+            << "\n\tx.nc():    " << x.nc()
+        );
+
+        T g, g2, s, Hg, gH;
+        double alpha = 10;
+
+        matrix<double,T::NR,T::NR> H(x.nr(),x.nr());
+        T delta, gamma;
+
+        H = identity_matrix<double>(H.nr());
+
+        g = der(x);
+
+        double f_value = min_f - 1;
+        double old_f_value = 0;
+
+        // loop until the derivative is almost zero
+        while(std::abs(old_f_value - f_value) > min_delta)
+        {
+            old_f_value = f_value;
+
+            s = -H*g;
+
+            alpha = line_search(make_line_search_function(f,x,s),make_line_search_function(der,x,s),0.01, 0.9,min_f, f_value);
+
+            x += alpha*s;
+
+
+            g2 = der(x);
+
+            // update H with the BFGS formula from (3.2.12) on page 55 of Fletcher 
+            delta = alpha*s;
+            gamma = g2-g;
+
+            Hg = H*gamma;
+            gH = trans(trans(gamma)*H);
+            double gHg = trans(gamma)*H*gamma;
+            double dg = trans(delta)*gamma;
+            if (gHg < std::numeric_limits<double>::infinity() && dg < std::numeric_limits<double>::infinity() &&
+                dg != 0)
+            {
+                H += (1 + gHg/dg)*delta*trans(delta)/(dg) - (delta*trans(gH) + Hg*trans(delta))/(dg);
+            }
+            else
+            {
+                H = identity_matrix<double>(H.nr());
+            }
+
+            g.swap(g2);
+        }
+
+        return f_value;
+    }
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct,
+        typename funct_der,
+        typename T
+        >
+    double conjugate_gradient (
+        const funct& f,
+        const funct_der& der,
+        T& x,
+        double min_f,
+        double min_delta = 1e-7
+    )
+    {
+        COMPILE_TIME_ASSERT(is_matrix<T>::value);
+        DLIB_ASSERT (
+            min_delta >= 0 && x.nc() == 1,
+            "\tdouble quasi_newton()"
+            << "\n\tYou have to supply column vectors to this function"
+            << "\n\tmin_delta: " << min_delta
+            << "\n\tx.nc():    " << x.nc()
+        );
+
+        T g, g2, s;
+        double alpha = 0;
+
+        g = der(x);
+        s = -g;
+
+        double f_value = min_f - 1;
+        double old_f_value = 0;
+
+        // loop until the derivative is almost zero
+        while(std::abs(old_f_value - f_value) > min_delta)
+        {
+            old_f_value = f_value;
+
+            alpha = line_search(make_line_search_function(f,x,s),make_line_search_function(der,x,s),0.001, 0.010,min_f, f_value);
+            x += alpha*s;
+
+
+            g2 = der(x);
+
+            // Use the Polak-Ribiere (4.1.12) conjugate gradient described by Fletcher on page 83
+            double b = trans(g2-g)*g2/(trans(g)*g);
+            s = -g2 + b*s;
+
+            g.swap(g2);
+        }
+
+        return f_value;
+    }
+
+// ----------------------------------------------------------------------------------------
+
+}
+
+#endif // DLIB_OPTIMIZATIOn_H_
+

dlib/optimization/optimization_abstract.h

+// Copyright (C) 2008  Davis E. King (davisking@users.sourceforge.net)
+// License: Boost Software License   See LICENSE.txt for the full license.
+#undef DLIB_OPTIMIZATIOn_ABSTRACT_
+#ifdef DLIB_OPTIMIZATIOn_ABSTRACT_
+
+#include <cmath>
+#include <limits>
+#include "../matrix/matrix_abstract.h"
+#include "../algs.h"
+
+
+namespace dlib
+{
+
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+//                    Functions that transform other functions  
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct
+        >
+    class central_differences;
+    /*!
+        This is a function object that represents the derivative of some other
+        function. 
+    !*/
+
+    template <
+        typename funct
+        >
+    const central_differences<funct> derivative(
+        const funct& f, 
+        double eps
+    );
+    /*!
+        requires
+            - f == a function that returns a scalar
+            - f must take either double or a dlib::matrix that is a column vector
+        ensures
+            - returns a function that represents the derivative of the function f.  It
+              is approximated numerically by:
+                  (f(x+eps)-f(x-eps))/(2*eps)
+    !*/
+
+    template <
+        typename funct
+        >
+    const central_differences<funct> derivative(
+        const funct& f
+    );
+    /*!
+        ensures
+            - returns derivative(f, 1e-7)
+    !*/
+
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename T
+        >
+    class line_search_funct; 
+    /*!
+        This is a function object l(double x) == f(start + x*direction).  That is, it 
+        represents the function l(double x) and takes f, start, and direction as arguments.
+    !*/
+
+    template <
+        typename funct, 
+        typename T
+        >
+    const line_search_funct<funct,T> make_line_search_function (
+        const funct& f, 
+        const T& start, 
+        const T& direction
+    ); 
+    /*!
+        requires
+            - f == a function that returns a scalar
+            - f must take a dlib::matrix that is a column vector
+            - is_matrix<T>::value == true (i.e. T must be a dlib::matrix)
+            - start.nc() == 1  
+            - direction.nc() == 1
+              (i.e. start and direction should be column vectors)
+            - f(start + 1.5*direction) should be a valid expression that
+              evaluates to a double
+        ensures
+            - returns a function that represents the function l(double x) 
+              that is defined as:
+                - l(x) == f(start + x*direction)
+    !*/
+
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+//                    Functions that perform unconstrained optimization 
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+
+    inline double poly_min_extrap (
+        double f0,
+        double d0,
+        double f1,
+        double d1
+    );
+    /*!
+        ensures
+            - let c(x) be a 3rd degree polynomial such that:
+                - c(0) == f0
+                - c(1) == f1
+                - derivative of c(x) at x==0 is d0
+                - derivative of c(x) at x==1 is d1
+            - returns the point in the range [0,1] that minimizes the polynomial c(x) 
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename funct_der
+        >
+    double line_search (
+        const funct& f, 
+        const funct_der& der, 
+        double rho, 
+        double sigma, 
+        double minf,
+        double& f0_out
+    );
+    /*!
+        requires
+            - 1 > sigma > rho > 0
+            - f and der are scalar functions of scalars
+              (e.g. line_search_funct objects)
+            - der is the derivative of f
+        ensures
+            - returns a value alpha such that f(alpha) is
+              significantly closer to the minimum of f than f(0).
+            - bigger values of sigma result in a less accurate but faster line search
+            - f0_out == f(0)
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename funct_der, 
+        typename T
+        >
+    double quasi_newton (
+        const funct& f, 
+        const funct_der& der, 
+        T& x, 
+        double min_f, 
+        double min_delta = 1e-7 
+    );
+    /*!
+        requires
+            - min_delta >= 0 
+            - f(x) must be a valid expression that evaluates to a double
+            - der(x) must be a valid expression that evaluates to the derivative of
+              f() at x.
+            - is_matrix<T>::value == true (i.e. T must be a dlib::matrix type)
+            - x.nc() == 1 (i.e. x must be a column vector)
+        ensures
+            - Performs an unconstrained minimization of the function f() using a 
+              quasi newton method.  The optimization stops when any of the following
+              conditions are satisfied: 
+                - the change in f() from one iteration to the next is less than min_delta
+                - f(#x) <= min_f
+            - #x == the value of x that was found to minimize f()
+            - returns f(#x) 
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename funct, 
+        typename funct_der, 
+        typename T
+        >
+    double conjugate_gradient (
+        const funct& f, 
+        const funct_der& der, 
+        T& x, 
+        double min_f, 
+        double min_delta = 1e-7
+    );
+    /*!
+        requires
+            - min_delta >= 0 
+            - f(x) must be a valid expression that evaluates to a double
+            - der(x) must be a valid expression that evaluates to the derivative of
+              f() at x.
+            - is_matrix<T>::value == true (i.e. T must be a dlib::matrix type)
+            - x.nc() == 1 (i.e. x must be a column vector)
+        ensures
+            - Performs an unconstrained minimization of the function f() using a 
+              quasi newton method.  The optimization stops when any of the following
+              conditions are satisfied: 
+                - the change in f() from one iteration to the next is less than min_delta
+                - f(#x) <= min_f
+            - #x == the value of x that was found to minimize f()
+            - returns f(#x) 
+    !*/
+
+// ----------------------------------------------------------------------------------------
+
+}
+
+#endif // DLIB_OPTIMIZATIOn_ABSTRACT_
+
+
+