#include "linear.h"
#include <stdlib.h>

long point_v[1024] = {0};
long point_l[1024] = {0};
int point_cnt = 0;
double k = 0;
double b = 0;
double theory_point[1024] = {0};
double linearity = 0;

extern double fabs(double __x);

/// <LinearFit>
/// 利用两点法进行线性拟合 y = kx + b,
/// <x,y—存放长度与电压的数组>
void linear_fit()
{
    // Ax+By+C=0
    double A = 0;
    double B = 0;
	double C = 0;
    int m = point_cnt; 

    A = point_v[m - 1] - point_v[0];
    B = point_l[0] - point_l[m-1];
	C = point_l[m - 1] * point_v[0] - point_l[0] * point_v[m - 1];

    k = -(A / B);
	b = -(C / B);
}

/// <summary>
/// 更新数组y，替换为电压理论值
void linear_val()
{
    for (int i = 0; i < point_cnt; i++)
    {
        theory_point[i] = k * point_l[i] + b;
    }
}	


void get_linearity()
{
	double max_bias = 0;
	
	linear_fit();
	linear_val();
	for (int i = 0; i < point_cnt; i++)
    {
        if(fabs(max_bias) < fabs(point_v[i] - theory_point[i]))
		{
			max_bias = point_v[i] - theory_point[i];
		}	
    }
	linearity = fabs(max_bias / (point_v[point_cnt-1] - point_v[0]));
}