#include <vector>
#include "LineFit.h"

bool LineFit(const std::vector<float> x, const std::vector<float> y, int size, double &k, double &b)
{
	if (size < 2)
	{
		k = 0;
		b = 0;
		return false;
	}
	double x_mean = 0;
	double y_mean = 0;
	for (int i = 0; i < size; i++)
	{
		x_mean += x[i];
		y_mean += y[i];
	}
	x_mean /= size;
	y_mean /= size;

	double Dxx = 0, Dxy = 0, Dyy = 0;

	for (int i = 0; i < size; i++)
	{
		Dxx += (x[i] - x_mean) * (x[i] - x_mean);
		Dxy += (x[i] - x_mean) * (y[i] - y_mean);
		Dyy += (y[i] - y_mean) * (y[i] - y_mean);
	}

	double lambda = ((Dxx + Dyy) - sqrt((Dxx - Dyy) * (Dxx - Dyy) + 4 * Dxy * Dxy)) / 2.0;
	double den = sqrt(Dxy * Dxy + (lambda - Dxx) * (lambda - Dxx));
	k = Dxy / (Dxx - lambda);
	b = (Dxy * x_mean) / (lambda - Dxx) + y_mean;
	return true;
}