说明：  趋势面分析是拟合数学曲面的一种统计方法。通常要找到一个合适的曲面精确表达实际问题往往比较困难，但却可以利用多项式函数来近似逼近它。
(trend surface analysis is fitting surfaces of a mathematical statistical methods. Usually to find a suitable surface accurately reflect the actual problems are often more difficult, but polynomial function can be used to approximating it.)