中文说明：
返回系数估计向量；stats返回各种参数估计；’wfun’指定一个加权函数；tune为调协常数；’const’的值为’on’(默认值)时添加一个常数项；为’off ’时忽略常数项
English Description：
Return coefficient estimation vector; Stats returns various parameter estimates; ' Wfun 'specifies a weighting function; Tune is the coordination constant; ' Add a constant item when the value of const 'is' on' (default value); Constant term ignored when 'off'