linearloss/turningPoint.cpp

#include <iostream>

void linear(double *x, double *y, int len, double *k, double *b)
{
    if (len < 2)
    {
        return;
    }
    double xsum = 0;
    double ysum = 0;
    double xysum = 0;
    double x2sum = 0;
    for (int i = 0; i < len; i++)
    {
        xsum += x[i];
        ysum += y[i];
        xysum += x[i] * y[i];
        x2sum += x[i] * x[i];
    }
    double xbar = xsum / len;
    double ybar = ysum / len;
    double xybar = xysum / len;
    double x2bar = x2sum / len;
    *k = (xybar - xbar * ybar) / (x2bar - xbar * xbar);
    *b = ybar - (*k) * xbar;
}

double loss(double *x, double *y, int len)
{
    double k, b;
    linear(x, y, len, &k, &b);
    double losssum = 0;
    for (int i = 0; i < len; i++)
    {
        losssum += (k * x[i] + b - y[i]) * (k * x[i] + b - y[i]);
    }
    double lossavg = losssum / len;
    return lossavg;
}

double *lossline(double *x, double *y, int len)
{
    int i = 1;
    double *losspoint = (double *)malloc(sizeof(double) * len);
    for (; i < len; i++)
    {
        losspoint[i - 1] = loss(x, y, i + 1);
    }
    return losspoint;
}

void mysort(double *x, double *y, int len)
{
    for (int i = 0; i < len; i++)
    {
        for (int j = 0; j < i; j++)
        {
            if (x[i] < x[j])
            {
                double temp = x[i];
                x[i] = x[j];
                x[j] = temp;
                temp = y[i];
                y[i] = y[j];
                y[j] = temp;
            }
        }
    }
}

void pointat(double *x, double *y, int len, int *result)
{
    mysort(x, y, len);
    double *ll = lossline(x, y, len);
    double *smothll = (double *)malloc(len * sizeof(double));
    for (int i = 0; i < len; i++)
    {
        int start = i - 5;
        int end = i + 5;
        if (start < 0)
        {
            start = 0;
        }
        if (end > len)
        {
            end = len;
        }
        double sum = 0;
        for (int count = start; count < end; count++)
        {
            sum += ll[count];
        }
        smothll[i] = sum / (end - start);
    }
    double *a = (double *)malloc(sizeof(double) * len - 10);
    for (int i = 5; i < len - 5; i++)
    {
        int s1 = 0;
        for (int j = i - 5; j < i + 5; j++)
        {
            s1 += smothll[j];
        }
        s1 = s1 - 10 * smothll[i];
        a[i - 5] = s1;
    }

    int index = 5;
    double max = a[0];
    for (int i = 0; i < len - 10; i++)
    {
        if (a[i] > max)
        {
            max = a[i];
            index = i + 5;
        }
    }
    *result = index;
}