listSquareMethod 最小二乘法拟合曲线 计算公式:https://blog.csdn.net/einstein10147/article/details/79205109 求解线性方程组:高斯消元. https://wenku.baidu.com/view/a58b31953086bceb19e8b8f67c1cfad6195fe9c3.html 计算R^2,决定系数: