#includedouble corr ( double x[], double y[], long n ) { double sum_x, sum_y, sum_xx, sum_yy, sum_xy; long i; sum_x = sum_y = sum_xx = sum_yy = sum_xy = 0.0; for ( i = 0; i < n; i++ ) { sum_x += x[i]; sum_y += y[i]; sum_xx += x[i]*x[i]; sum_yy += y[i]*y[i]; sum_xy += x[i]*y[i]; } return (n*sum_xy-sum_x*sum_y)/ sqrt((n*sum_xx-sum_x*sum_x)*(n*sum_yy-sum_y*sum_y)); }