3

单调递减

${\alpha }_1<0$

${\alpha }_2=0$

${\alpha }_3=0$

4

U形

${\alpha }_1<0$

${\alpha }_2>0$

${\alpha }_3=0$

5

水平线

${\alpha }_1=0$

${\alpha }_2=0$

${\alpha }_3=0$

6

倒N形

${\alpha }_1<0$

${\alpha }_2>0$

${\alpha }_3<0$

7

N形

${\alpha }_1>0$

${\alpha }_2<0$

${\alpha }_3>0$

8

倒U形 + U形

${\alpha }_1<0$

${\alpha }_2<0$

${\alpha }_3>0$