$$w（n）＝｛\begin{array}{ll}\frac{2n}{l+1}\hfill & 1\le n\le \frac{l+1}{2}\hfill \\ 2-\frac{2n}{l+1}\hfill & \frac{l+1}{2}+1\le n\le l\hfill \end{array}$$

$$w（n）＝｛\begin{array}{ll}\frac{（2n-1）}{l}\hfill & 1\le n\le \frac{l}{2}\hfill \\ 2-\frac{（2n-1）}{l}\hfill & \frac{l}{2}+1\le n\le l\hfill \end{array}$$