如何在C ++中找到两个向量之间的最小（优化）距离

问题描述 投票：2回答：2

我正在将Python的'page_dewarper'（https://mzucker.github.io/2016/08/15/page-dewarping.html）版本翻译成C ++。我将使用dlib，这是一个很棒的工具，它帮助我解决了一些优化问题。在Github repo（https://github.com/mzucker/page_dewarp/blob/master/page_dewarp.py）的第748行中，Matt使用Scipy的优化函数来找到两个向量之间的最小距离。我认为，我的C ++等价物应该是solve_least_squares_lm（）或solve_least_squares（）。我将举一个具体的例子进行分析。

我的数据： a）dstpoints是一个带有OpenCV点的向量 - std::vector<cv::Point2f>（在这个例子中我有162个点，它们没有变化）， b）ppts也是std::vector<cv::Point2f>，大小与dstpoints相同。

std::vector<cv::Point2f> ppts = project_keypoints(params, input);

它取决于： - dlib::column_vector'输入'是2 * 162 = 324长并且没有变化， - dlib::column_vector'params'是189长并且它的值应该被改变以获得变量'suma'的最小值，如下所示：

    double suma = 0.0;
    for (int i=0; i<dstpoints_size; i++)
    {
        suma += pow(dstpoints[i].x - ppts[i].x, 2);
        suma += pow(dstpoints[i].y - ppts[i].y, 2);
    }

我正在寻找'params'向量，它会给我'suma'变量的最小值。最小二乘算法似乎是解决它的一个很好的选择：http://dlib.net/dlib/optimization/optimization_least_squares_abstract.h.html#solve_least_squares，但我不知道它对我的情况是否有益。 我想，我的问题是，对于每个不同的'params'向量，我得到不同的'ppts'向量，不仅是单个值，而且我不知道solve_least_squares函数是否可以匹配我的例子。 我必须为每一点计算残差。我想，上面提到的链接中的'list'应该是这样的：

(ppts[i].x - dstpoints[i].x, ppts[i].y - dstpoints[i].y, ppts[i+1].x - dstpoints[i+1].x, ppts[i+1].y - dstpoints[i+1].y, etc.)

，'ppts'向量依赖于'params'向量，然后这个问题可以用最小二乘算法解决。我不知道如何使用这些假设创建data_samples，因为它需要每个样本使用dlib::input_vector，如示例所示：http://dlib.net/least_squares_ex.cpp.html。 我在想吗？

c++ dlib least-squares
2个回答
0
投票

这几天我也在做同样的事情。我的解决方案是自己写一个鲍威尔课程。它工作，但真的很慢。该程序在dewarping linguistics_thesis.jpg中需要2分钟。我不知道程序运行得如此缓慢的原因。也许是因为算法或代码有一些额外的循环。我是中国学生，我的学校只有java课程。因此，如果您在我的代码中找到一些额外的代码，这是正常的。这是我的鲍威尔课程。

using namespace std;
using namespace cv;
class MyPowell
{
public:
    vector<vector<double>> xi;
    vector<double> pcom;
    vector<double> xicom;

    vector<Point2d> dstpoints;
    vector<double> myparams;
    vector<double> params;
    vector<Point> keypoint_index;

    Point2d dst_br;
    Point2d dims;
    int N;
    int itmax;
    int ncom;
    int iter;
    double fret, ftol;

    int usingAorB;

    MyPowell(vector<Point2d> &dstpoints, vector<double> &params, vector<Point> &keypoint_index);
    MyPowell(Point2d &dst_br, vector<double> &params, Point2d & dims);
    MyPowell();
    double obj(vector<double> &params);

    void powell(vector<double> &p, vector<vector<double>> &xi, double ftol, double &fret);

    double sign(double a);// , double b);
    double sqr(double a);

    void linmin(vector<double> &p, vector<double> &xit, int n, double &fret);
    void mnbrak(double & ax, double & bx, double & cx,
        double & fa, double & fb, double & fc);
    double f1dim(double x);
    double brent(double ax, double bx, double cx, double & xmin, double tol);

    vector<double> usePowell();

    void erase(vector<double>& pbar, vector<double> &prr, vector<double> &pr);
};


#include"Powell.h"

MyPowell::MyPowell(vector<Point2d> &dstpoints, vector<double>& params, vector<Point> &keypoint_index)
{
    this->dstpoints = dstpoints;
    this->myparams = params;
    this->keypoint_index = keypoint_index;

    N = params.size();
    itmax = N * N;
    usingAorB = 1;
}

MyPowell::MyPowell(Point2d & dst_br, vector<double>& params, Point2d & dims)
{
    this->dst_br = dst_br;
    this->myparams.push_back(dims.x);
    this->myparams.push_back(dims.y);
    this->params = params;
    this->dims = dims;

    N = 2;
    itmax = N * 1000;
    usingAorB = 2;
}

MyPowell::MyPowell()
{
    usingAorB = 3;

}

double MyPowell::obj(vector<double> &myparams)
{
    if (1 == usingAorB)
    {
        vector<Point2d> ppts = Dewarp::projectKeypoints(keypoint_index, myparams);

        double total = 0;
        for (int i = 0; i < ppts.size(); i++)
        {
            double x = dstpoints[i].x - ppts[i].x;
            double y = dstpoints[i].y - ppts[i].y;
            total += (x * x + y * y);
        }
        return total;
    }
    else if(2 == usingAorB)
    {
        dims.x = myparams[0];
        dims.y = myparams[1];
        //cout << "dims.x " << dims.x << "  dims.y " << dims.y << endl;
        vector<Point2d> vdims = { dims };
        vector<Point2d> proj_br = Dewarp::projectXY(vdims, params);

        double total = 0;

        double x = dst_br.x - proj_br[0].x;
        double y = dst_br.y - proj_br[0].y;
        total += (x * x + y * y);

        return total;
    }
    return 0;
}

void MyPowell::powell(vector<double> &x, vector<vector<double>> &direc, double ftol, double &fval)
{
    vector<double> x1;
    vector<double> x2;
    vector<double> direc1;
    int myitmax = 20;
    if(N>500)
        myitmax = 10;
    else if (N > 300)
    {
        myitmax = 15;
    }
    double fx2, t, fx, dum, delta;
    fval = obj(x);
    int bigind;
    for (int j = 0; j < N; j++)
    {
        x1.push_back(x[j]);
    }
    int iter = 0;

    while (true)
    {
        do
        {
            do
            {
                iter += 1;
                fx = fval;
                bigind = 0;
                delta = 0.0;
                for (int i = 0; i < N; i++)
                {
                    direc1 = direc[i];
                    fx2 = fval;
                    linmin(x, direc1, N, fval);
                    if (fabs(fx2 - fval) > delta)
                    {
                        delta = fabs(fx2 - fval);
                        bigind = i;
                    }
                }
                if (2.0 * fabs(fx - fval) <= ftol * (fabs(fx) + fabs(fval)) + 1e-7)
                {
                    erase(direc1, x2, x1);
                    return;
                }
                if (iter >= itmax)
                {
                    cout << "powell exceeding maximum iterations" << endl;
                    return;
                }
                if (!x2.empty())
                {
                    x2.clear();
                }
                for (int j = 0; j < N; j++)
                {
                    x2.push_back(2.0*x[j] - x1[j]);
                    direc1[j] = x[j] - x1[j];
                    x1[j] = x[j];
                }
                myitmax--;
                cout << fx2 << endl;
                fx2 = obj(x2);
                if (myitmax < 0)
                    return;
            } while (fx2 >= fx);

            dum = fx - 2 * fval + fx2;
            t = 2.0*dum*pow((fx - fval - delta), 2) - delta * pow((fx - fx2), 2);

        } while (t >= 0.0);
        linmin(x, direc1, N, fval);
        direc[bigind] = direc1;
    } 
}

double MyPowell::sign(double a)//, double b)
{
    if (a > 0.0)
    {
        return 1;
    }
    else
    {
        if (a < 0.0)
        {
            return -1;
        }
    }
    return 0;
}

double MyPowell::sqr(double a)
{
    return a * a;
}

void MyPowell::linmin(vector<double>& p, vector<double>& xit, int n, double &fret)
{
    double tol = 1e-2;
    ncom = n;
    pcom = p;
    xicom = xit;
    double ax = 0.0;
    double xx = 1.0;
    double bx = 0.0;
    double fa, fb, fx, xmin;
    mnbrak(ax, xx, bx, fa, fx, fb);
    fret = brent(ax, xx, bx, xmin, tol);
    for (int i = 0; i < n; i++)
    {
        xit[i] = (xmin * xit[i]);
        p[i] += xit[i];
    }
}

void MyPowell::mnbrak(double & ax, double & bx, double & cx, 
    double & fa, double & fb, double & fc)
{
    const double GOLD = 1.618034, GLIMIT = 110.0, TINY = 1e-20;
    double val, fw, tmp2, tmp1, w, wlim;
    double denom;
    fa = f1dim(ax);
    fb = f1dim(bx);
    if (fb > fa)
    {
        val = ax;
        ax = bx;
        bx = val;
        val = fb;
        fb = fa;
        fa = val;
    }
    cx = bx + GOLD * (bx - ax);
    fc = f1dim(cx);
    int iter = 0;
    while (fb >= fc)
    {
        tmp1 = (bx - ax) * (fb - fc);
        tmp2 = (bx - cx) * (fb - fa);
        val = tmp2 - tmp1;
        if (fabs(val) < TINY)
        {
            denom = 2.0*TINY;
        }
        else
        {
            denom = 2.0*val;
        }
        w = bx - ((bx - cx)*tmp2 - (bx - ax)*tmp1) / (denom);
        wlim = bx + GLIMIT * (cx - bx);
        if ((bx - w) * (w - cx) > 0.0)
        {
            fw = f1dim(w);
            if (fw < fc)
            {
                ax = bx;
                fa = fb;
                bx = w;
                fb = fw;
                return;
            }
            else if (fw > fb)
            {
                cx = w;
                fc = fw;
                return;
            }
            w = cx + GOLD * (cx - bx);
            fw = f1dim(w);
        }
        else 
        {
            if ((cx - w)*(w - wlim) >= 0.0)
            {
                fw = f1dim(w);
                if (fw < fc)
                {
                    bx = cx;
                    cx = w;
                    w = cx + GOLD * (cx - bx);
                    fb = fc;
                    fc = fw;
                    fw = f1dim(w);
                }
            }
            else if ((w - wlim)*(wlim - cx) >= 0.0)
            {
                w = wlim;
                fw = f1dim(w);
            }
            else
            {
                w = cx + GOLD * (cx - bx);
                fw = f1dim(w);
            }
        }

        ax = bx;
        bx = cx;
        cx = w;
        fa = fb;
        fb = fc;
        fc = fw;
    }
}

double MyPowell::f1dim(double x)
{
    vector<double> xt;
    for (int j = 0; j < ncom; j++)
    {
        xt.push_back(pcom[j] + x * xicom[j]);
    }
    return obj(xt);
}

double MyPowell::brent(double ax, double bx, double cx, double & xmin, double tol = 1.48e-8)
{
    const double CGOLD = 0.3819660, ZEPS = 1.0e-4;
    int itmax = 500;
    double a = MIN(ax, cx);
    double b = MAX(ax, cx);
    double v = bx;
    double w = v, x = v;
    double deltax = 0.0;
    double fx = f1dim(x);
    double fv = fx;
    double fw = fx;
    double rat = 0, u = 0, fu;
    int iter;
    int done;
    double dx_temp, xmid, tol1, tol2, tmp1, tmp2, p;
    for (iter = 0; iter < 500; iter++)
    {
        xmid = 0.5 * (a + b);
        tol1 = tol * fabs(x) + ZEPS;
        tol2 = 2.0*tol1;
        if (fabs(x - xmid) <= (tol2 - 0.5*(b - a)))
            break;
        done = -1;
        if (fabs(deltax) > tol1)
        {
            tmp1 = (x - w) * (fx - fv);
            tmp2 = (x - v) * (fx - fw);
            p = (x - v) * tmp2 - (x - w) * tmp1;
            tmp2 = 2.0 * (tmp2 - tmp1);
            if (tmp2 > 0.0)
                p = -p;
            tmp2 = fabs(tmp2);
            dx_temp = deltax;
            deltax = rat;
            if ((p > tmp2 * (a - x)) && (p < tmp2 * (b - x)) &&
                fabs(p) < fabs(0.5 * tmp2 * dx_temp))
            {
                rat = p / tmp2;
                u = x + rat;
                if ((u - a) < tol2 || (b - u) < tol2)
                {
                    rat = fabs(tol1) * sign(xmid - x);
                }
                done = 0;
            }

        }
        if(done)
        {
            if (x >= xmid)
            {
                deltax = a - x;
            }
            else
            {
                deltax = b - x;
            }
            rat = CGOLD * deltax;
        }
        if (fabs(rat) >= tol1)
        {
            u = x + rat;
        }
        else
        {
            u = x + fabs(tol1) * sign(rat);
        }
        fu = f1dim(u);

        if (fu > fx)
        {
            if (u < x)
            {
                a = u;
            }
            else
            {
                b = u;
            }
            if (fu <= fw || w == x)
            {
                v = w;
                w = u;
                fv = fw;
                fw = fu;
            }
            else if (fu <= fv || v == x || v == w)
            {
                v = u;
                fv = fu;
            }
        }
        else
        {
            if (u >= x)
                a = x;
            else
                b = x;
            v = w;
            w = x;
            x = u;
            fv = fw;
            fw = fx;
            fx = fu;
        }
    }
    if(iter > itmax)
        cout << "\n Brent exceed maximum iterations.\n\n";
    xmin = x;
    return fx;
}

vector<double> MyPowell::usePowell()
{
    ftol = 1e-4;
    vector<vector<double>> xi;
    for (int i = 0; i < N; i++)
    {
        vector<double> xii;
        for (int j = 0; j < N; j++)
        {
            xii.push_back(0);
        }
        xii[i]=(1.0);
        xi.push_back(xii);
    }
    double fret = 0;
    powell(myparams, xi, ftol, fret);
    //for (int i = 0; i < xi.size(); i++)
    //{
    //  double a = obj(xi[i]);
    //  if (fret > a)
    //  {
    //      fret = a;
    //      myparams = xi[i];
    //  }
    //}
    cout << "final result" << fret << endl;
    return myparams;
}

void MyPowell::erase(vector<double>& pbar, vector<double>& prr, vector<double>& pr)
{
    for (int i = 0; i < pbar.size(); i++)
    {
        pbar[i] = 0;
    }
    for (int i = 0; i < prr.size(); i++)
    {
        prr[i] = 0;
    }
    for (int i = 0; i < pr.size(); i++)
    {
        pr[i] = 0;
    }
}
0
投票

我使用了PRAXIS库，因为它不需要衍生信息而且速度很快。我根据自己的需要修改了一些代码，现在它比用Python编写的原始版本更快。

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