aux_functions.h

#include <stdexcept>
#include <cmath>

using namespace std;

//calculating linear regression
void linear_fit(int data_size, double *x, double *y, double *slope, double *intercept, double *mean_x); 
double error_interval(double *x, double *y, double mean_x, int data_size, double slope, double intercept);
double error_update(int old_size, double *SSres, double *mean_x, double slope, double intercept, double *y, double *x); 
//calculating quantile
double quantile(double p); 
inline double inv_erf(double x); 
inline int sgn(double x);