Solution 4.6.2.2
The characteristic polynomial is
p(s)=s
6
+5s
5
+6s
4
+10s
3
+0s
2
+4s +1:
The initial Routh table is
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
b
1
b
2
b
3
0 0
s
3
c
1
c
2
c
3
0 0
s
2
d
1
d
2
d
3
0 0
s
1
e
1
e
2
e
3
0 0
s
0
f
1
f
2
f
3
0 0
.
Then
b
1
=
;Det
"
1 6
5 10
#
5
=
;(10;30)
5
=4;;
b
2
=
;Det
"
1 0
5 4
#
5
=
;(4;0)
5
= ;4=5
b
3
=
;Det
"
1 1
5 0
#
5
=
;(0;5)
5
=1
The partially completed Routh table is then
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
4 ;4=5 1 0 0
s
3
c
1
c
2
c
3
0 0
s
2
d
1
d
2
d
3
0 0
s
1
e
1
e
2
e
3
0 0
s
0
f
1
f
2
f
3
0 0
.
1
c
1
=
;Det
"
5 10
4 ;4=5
#
4
=
;(;4;40)
4
= 11
c
2
=
;Det
"
5 4
4 1
#
5
=
;(5;16)
5
= 16=5
c
3
=
;Det
"
5 0
4 0
#
5
=
;(0;0)
4
= 0
The Routh table is now:
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
4 ;4=5 1 0 0
s
3
11 16=5 0 0 0
s
2
d
1
d
2
d
3
0 0
s
1
e
1
e
2
e
3
0 0
s
0
f
1
f
2
f
3
0 0
.
d
1
=
;Det
"
4 ;4=5
11 16=5
#
11
=
;(64=5+44=5)
11
= ;108=55
2
d
2
=
;Det
"
4 1
11 0
#
11
= 1
d
3
=
;Det
"
4 0
11 0
#
11
= 0
The partially complete Routh arrayisnow
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
4 ;4=5 1 0 0
s
3
11 16=5 0 0 0
s
2
;108=55 1 0 0 0
s
1
e
1
e
2
e
3
0 0
s
0
f
1
f
2
f
3
0 0
.
e
1
=
;Det
"
11 16=5
;108=55 1
#
;108=55
= ;(11 + 1728=275)=(;108=55)
= 4753=540
e
2
=
;Det
"
11 0
;108=55 0
#
;108=55
= 0
e
3
=
;Det
"
11 0
;1;8=55 0
#
;108=55
= 0
The partially nished Routh table is now
3
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
4 ;4=5 1 0 0
s
3
11 16=5 0 0 0
s
2
;108=55 1 0 0 0
s
1
4753=540 0 0 0 0
s
0
f
1
f
2
f
3
0 0
.
f
1
=
;Det
"
;108=55 1
4753=540 0
#
4753=540
= ;
;4753=540
4753=540
= 1
f
2
=
;Det
"
;108=55 0
4753=540 0
#
4753=540
= 0
f
3
=
;Det
"
;108=55 0
4753=540 0
#
4753=540
= 0
The nal Routh table is
s
6
1 6 0 1 0
s
5
5 10 4 0 0
s
4
4 ;4=5 1 0 0
s
3
11 16=5 0 0 0
s
2
;108=55 1 0 0 0
s
1
4753=540 0 0 0 0
s
0
1 0 0 0 0
.
There are two sign changes, positivetonegativeand negativetopostiveas
wegofromrow4torow5t0row6.Thus there are tworoots in the right
half plane. This is veried by the MATLAB dialogure:
4
EDU>p = [1 5610041]
p=
1 5 6 10 0 4 1
EDU>roots(p)
ans =
-4.1474
-0.5655+ 1.4611i
-0.5655- 1.4611i
0.2515+ 0.6114i
0.2515- 0.6114i
-0.2248
EDU>
It is clear that a program likeMATLAB obviates muchofthe value of the
Routh criterion.
5