matlab简易逐步回归，内含2、3、4、5、6、8、10个因子回归时代码，对多因子进行排列组合，按照因子数进行回归，寻找最佳因子个数的回归方程。(Matlab simple step by step regression, containing 2, 3, 4, 5, 6, 8, 10 factors regression code, arranged on the multi-factor combination, regression in accordance with the number of factors to find the regression equation of the best number of factors.)