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Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

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Page 1: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

Lecture 5 - how to find a Lyapunov function? -

1

Page 2: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

What we already know...

2

Page 3: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

3

Page 4: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

CALIFORNIA INSTITUTE OF TECHNOLOGYControl and Dynamical Systems

CDS 110a

R. M. Murray Lyapunov Stability Analysis 17 October 2007

This lecture provides an overview of Lyapunov stability for time-invariant systems. We presenta survey of the main results that we shall need in the sequel; proofs are omitted, but can befound in standard texts such as Vidyasagar [2] or Khalil [1].

Reading:

• Astrom and Murray, Section 4.4

1 Basic definitions

Consider a closed loop dynamical system of the form

x = F (x) x ! Rn (1)

with equilibrium point xe ! Rn. We recall the following definition from Monday’s lecture:

Definition 1. An equlibrium point xe = 0 is locally asymptotically stable if

1. xe = 0 is stable in the sense of Lyapunov: for any ! > 0there exists " > 0 such that

"x(0)#xe" < " =$ "x(t)#xe" < ! for all t > 0.

2. xe = 0 is locally attractive: there exists " > 0 such that

"x(t0)" < " =$ limt!"

x(t) = 0

B!

B"

2 Lyapunov Stability

Definition 2. A continuous function V : Rn % R is (locally) positive definite if for some r > 0

V (0) = 0 and V (x) > 0 for all x &= 0 and "x" < r.

V is (locally) positive semi-definite if for some r > 0

V (0) = 0 and V (x) ' 0 for all "x" < r.

V is globally positive (semi-) definite if these statements are true for all x ! R.

Review

4

Page 5: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

5

x1

x2

x1 = 2x1x2

x2 = x22 � x2

1

Why capture the notion of stability?

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3

Page 6: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

CALIFORNIA INSTITUTE OF TECHNOLOGYControl and Dynamical Systems

CDS 110a

R. M. Murray Lyapunov Stability Analysis 17 October 2007

This lecture provides an overview of Lyapunov stability for time-invariant systems. We presenta survey of the main results that we shall need in the sequel; proofs are omitted, but can befound in standard texts such as Vidyasagar [2] or Khalil [1].

Reading:

• Astrom and Murray, Section 4.4

1 Basic definitions

Consider a closed loop dynamical system of the form

x = F (x) x ! Rn (1)

with equilibrium point xe ! Rn. We recall the following definition from Monday’s lecture:

Definition 1. An equlibrium point xe = 0 is locally asymptotically stable if

1. xe = 0 is stable in the sense of Lyapunov: for any ! > 0there exists " > 0 such that

"x(0)#xe" < " =$ "x(t)#xe" < ! for all t > 0.

2. xe = 0 is locally attractive: there exists " > 0 such that

"x(t0)" < " =$ limt!"

x(t) = 0

B!

B"

2 Lyapunov Stability

Definition 2. A continuous function V : Rn % R is (locally) positive definite if for some r > 0

V (0) = 0 and V (x) > 0 for all x &= 0 and "x" < r.

V is (locally) positive semi-definite if for some r > 0

V (0) = 0 and V (x) ' 0 for all "x" < r.

V is globally positive (semi-) definite if these statements are true for all x ! R.

Review

6

Page 7: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

Type of stability: Lyapunov theory

7

Remarks:

1. To see the di!erence between positive definite and positive semi-definite, suppose that x ! R2

and letV1(x) = x2

1 V2(x) = x21 + x2

2.

Both V1 and V2 are always non-negative. However, it is possible for V1 to be zero even ifx "= 0. Specifically, if we set x = (0, c) where c ! R is any non-zero number, then V1(x) = 0.On the other hand, V2(x) = 0 if and only if x = (0, 0). Thus V1(x) is positive semi-definiteand V2(x) is positive definite.

Theorem 1. Let V be a non-negative function on Rn and let V represent the time derivative of V

along trajectories of the system dynamics (1):

V =!V

!x

dx

dt=

!V

!xF (x).

Let Br = Br(0) be a ball of radius r around the origin. If there exists r > 0 such that V ispositive definite and V is negative semi-definite for all x ! Br, then x = 0 is locally stable in thesense of Lyapunov. If V is positive definite and V is negative definite in Br, then x = 0 is locallyasymptotically stable.

Remarks

1. A function V satisfying the conditions of the theorem is called a Lyapunov function.

2. V (x) is an “energy like” function that bounds the size of x.

V (x) = c1

dx

dt

!V

!x

V (x) = c1

Example 1.

x1 = #x1 # x2 V (x) = x21 + x2

2 > 0 $x "= 0

x2 = #x2 V (x) = 2x1x1 + 2x2x2

= #2x21 # 2x1x2 # 2x2

2

= #(x1 + x2)2 # x2

1 # x22 < 0 $x "= 0

=% globally asymptotically stable.

2

stable in the

Page 8: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

How to find a Lyapunov function?• In general (linear + non-linear systems):

- Before guess (before 2000) - Now use SOS-tools (Matlab toolbox) for polynomial

systems with known coefficients

How about for linear systems?

8

Page 9: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

• For linear systems: • Let • V positive definite ⇔ P positive definite matrix (P > 0)

• Compute its derivative:

• Let

• Solve for P in

To fix this problem, we skew the level sets slightly, so that the flow of the system crosses the levelsurfaces transversely. Define

V (x, t) = 12

!

q

q

"T !

k !m

!m m

" !

q

q

"

= 12 qmq + 1

2qkq + !qmq,

where ! is a small positive constant such that V is still positive definite. The derivative of theLyapunov function becomes

V = qmq + qkq + !mq2 + !qmq

= (!c + !m)q2 + !(!kq2 ! cqq) = !

!

q

q

"T !

!k 12!c

12!c c ! !m

" !

q

q

"

.

The function V can be made negative definite for ! chosen su!ciently small (exercise) and hencewe can conclude exponential stability.

Remarks

1. As the previous example shows, a Lyapunov function need not be unique and di"erent Lya-punov functions can give stronger stability results.

2. Lyapunov functions can also be used to prove that a system is unstable: search for V positivedefinite with V positive definite.

3 Lyapunov Functions for Linear Systems

Consider a linear system of the formx = Ax.

Search for a quadratic Lyapunov function

V (x) = xT Px

Compute the derivativedV

dt=

"V

"x

dx

dt= xT (AT P + PA)x.

The requirement that V is positive definite is equivalent to P > 0 and the requirement that V isnegative definite becomes a condition that

Q = AT P + PA < 0 (2)

(as a matrix).

Trick: equation (2) is linear in P . So we can choose Q < 0 and the solve for P .

4

To fix this problem, we skew the level sets slightly, so that the flow of the system crosses the levelsurfaces transversely. Define

V (x, t) = 12

!

q

q

"T !

k !m

!m m

" !

q

q

"

= 12 qmq + 1

2qkq + !qmq,

where ! is a small positive constant such that V is still positive definite. The derivative of theLyapunov function becomes

V = qmq + qkq + !mq2 + !qmq

= (!c + !m)q2 + !(!kq2 ! cqq) = !

!

q

q

"T !

!k 12!c

12!c c ! !m

" !

q

q

"

.

The function V can be made negative definite for ! chosen su!ciently small (exercise) and hencewe can conclude exponential stability.

Remarks

1. As the previous example shows, a Lyapunov function need not be unique and di"erent Lya-punov functions can give stronger stability results.

2. Lyapunov functions can also be used to prove that a system is unstable: search for V positivedefinite with V positive definite.

3 Lyapunov Functions for Linear Systems

Consider a linear system of the formx = Ax.

Search for a quadratic Lyapunov function

V (x) = xT Px

Compute the derivativedV

dt=

"V

"x

dx

dt= xT (AT P + PA)x.

The requirement that V is positive definite is equivalent to P > 0 and the requirement that V isnegative definite becomes a condition that

Q = AT P + PA < 0 (2)

(as a matrix).

Trick: equation (2) is linear in P . So we can choose Q < 0 and the solve for P .

4

To fix this problem, we skew the level sets slightly, so that the flow of the system crosses the levelsurfaces transversely. Define

V (x, t) = 12

!

q

q

"T !

k !m

!m m

" !

q

q

"

= 12 qmq + 1

2qkq + !qmq,

where ! is a small positive constant such that V is still positive definite. The derivative of theLyapunov function becomes

V = qmq + qkq + !mq2 + !qmq

= (!c + !m)q2 + !(!kq2 ! cqq) = !

!

q

q

"T !

!k 12!c

12!c c ! !m

" !

q

q

"

.

The function V can be made negative definite for ! chosen su!ciently small (exercise) and hencewe can conclude exponential stability.

Remarks

1. As the previous example shows, a Lyapunov function need not be unique and di"erent Lya-punov functions can give stronger stability results.

2. Lyapunov functions can also be used to prove that a system is unstable: search for V positivedefinite with V positive definite.

3 Lyapunov Functions for Linear Systems

Consider a linear system of the formx = Ax.

Search for a quadratic Lyapunov function

V (x) = xT Px

Compute the derivativedV

dt=

"V

"x

dx

dt= xT (AT P + PA)x.

The requirement that V is positive definite is equivalent to P > 0 and the requirement that V isnegative definite becomes a condition that

Q = AT P + PA < 0 (2)

(as a matrix).

Trick: equation (2) is linear in P . So we can choose Q < 0 and the solve for P .

4

9

V (x) = x>Px

How to find a Lyapunov function?

x>Px > 0 for all x 6= 0

Q < 0

Page 10: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

ExampleExample 3. Consider the linear system

dx1

dt= !ax1

dx2

dt= !bx1 ! cx2.

with a, b, c > 0, for which we have

A =

!

!a 0!b !c

"

P =

!

p11 p12

p21 p22

"

.

We choose Q = !I " R2!2 and the corresponding Lyapunov equation is

!

!a !b

0 !c

" !

p11 p12

p21 p22

"

+

!

p11 p12

p21 p22

" !

!a 0!b !c

"

=

!

1 00 1

"

and solving for the elements of P yields

P =

#

b2+ac+c2

2a2c+2ac2"b

2c(a+c)"b

2c(a+c)12

$

or

V (x) =b2 + ac + c2

2a2c + 2ac2x2

1 !b

c(a + c)x1x2 +

1

2x2

2.

It is easy to verify that P > 0 (check its eigenvalues) and by construction P = !I < 0. Hence thesystem is asymptotically stable.

4 Krasolvskii-Lasalle Invariance Principle (optional)

The Krasolvskii-Lasalle invariance principle provides a way to prove asymptotic stability when V

is negative semi-definite (which is usually much easier to find).

Denote the solution trajectories of the time-invariant system

dx

dt= F (x) (3)

as x(t; x0, t0), which is the solution of equation (3) at time t starting from x0 at t0. We writex(·; x0, t0) for the set of all points lying along the trajectory.Definition 3 (! limit set). The ! limit set of a trajectory x(·; x0, t0) is the set of all points z " Rn

such that there exists a strictly increasing sequence of times tn such that

s(tn; x0, t0) # z

as n # $.

5

Example 3. Consider the linear system

dx1

dt= !ax1

dx2

dt= !bx1 ! cx2.

with a, b, c > 0, for which we have

A =

!

!a 0!b !c

"

P =

!

p11 p12

p21 p22

"

.

We choose Q = !I " R2!2 and the corresponding Lyapunov equation is

!

!a !b

0 !c

" !

p11 p12

p21 p22

"

+

!

p11 p12

p21 p22

" !

!a 0!b !c

"

=

!

1 00 1

"

and solving for the elements of P yields

P =

#

b2+ac+c2

2a2c+2ac2"b

2c(a+c)"b

2c(a+c)12

$

or

V (x) =b2 + ac + c2

2a2c + 2ac2x2

1 !b

c(a + c)x1x2 +

1

2x2

2.

It is easy to verify that P > 0 (check its eigenvalues) and by construction P = !I < 0. Hence thesystem is asymptotically stable.

4 Krasolvskii-Lasalle Invariance Principle (optional)

The Krasolvskii-Lasalle invariance principle provides a way to prove asymptotic stability when V

is negative semi-definite (which is usually much easier to find).

Denote the solution trajectories of the time-invariant system

dx

dt= F (x) (3)

as x(t; x0, t0), which is the solution of equation (3) at time t starting from x0 at t0. We writex(·; x0, t0) for the set of all points lying along the trajectory.Definition 3 (! limit set). The ! limit set of a trajectory x(·; x0, t0) is the set of all points z " Rn

such that there exists a strictly increasing sequence of times tn such that

s(tn; x0, t0) # z

as n # $.

5

Example 3. Consider the linear system

dx1

dt= !ax1

dx2

dt= !bx1 ! cx2.

with a, b, c > 0, for which we have

A =

!

!a 0!b !c

"

P =

!

p11 p12

p21 p22

"

.

We choose Q = !I " R2!2 and the corresponding Lyapunov equation is

!

!a !b

0 !c

" !

p11 p12

p21 p22

"

+

!

p11 p12

p21 p22

" !

!a 0!b !c

"

=

!

1 00 1

"

and solving for the elements of P yields

P =

#

b2+ac+c2

2a2c+2ac2"b

2c(a+c)"b

2c(a+c)12

$

or

V (x) =b2 + ac + c2

2a2c + 2ac2x2

1 !b

c(a + c)x1x2 +

1

2x2

2.

It is easy to verify that P > 0 (check its eigenvalues) and by construction P = !I < 0. Hence thesystem is asymptotically stable.

4 Krasolvskii-Lasalle Invariance Principle (optional)

The Krasolvskii-Lasalle invariance principle provides a way to prove asymptotic stability when V

is negative semi-definite (which is usually much easier to find).

Denote the solution trajectories of the time-invariant system

dx

dt= F (x) (3)

as x(t; x0, t0), which is the solution of equation (3) at time t starting from x0 at t0. We writex(·; x0, t0) for the set of all points lying along the trajectory.Definition 3 (! limit set). The ! limit set of a trajectory x(·; x0, t0) is the set of all points z " Rn

such that there exists a strictly increasing sequence of times tn such that

s(tn; x0, t0) # z

as n # $.

5

10

�a �b0 �c

� p11 p12p21 p22

�+

p11 p12p21 p22

� �a 0�b �c

�=

�1 00 �1

Example 3. Consider the linear system

dx1

dt= !ax1

dx2

dt= !bx1 ! cx2.

with a, b, c > 0, for which we have

A =

!

!a 0!b !c

"

P =

!

p11 p12

p21 p22

"

.

We choose Q = !I " R2!2 and the corresponding Lyapunov equation is

!

!a !b

0 !c

" !

p11 p12

p21 p22

"

+

!

p11 p12

p21 p22

" !

!a 0!b !c

"

=

!

1 00 1

"

and solving for the elements of P yields

P =

#

b2+ac+c2

2a2c+2ac2"b

2c(a+c)"b

2c(a+c)12

$

or

V (x) =b2 + ac + c2

2a2c + 2ac2x2

1 !b

c(a + c)x1x2 +

1

2x2

2.

It is easy to verify that P > 0 (check its eigenvalues) and by construction P = !I < 0. Hence thesystem is asymptotically stable.

4 Krasolvskii-Lasalle Invariance Principle (optional)

The Krasolvskii-Lasalle invariance principle provides a way to prove asymptotic stability when V

is negative semi-definite (which is usually much easier to find).

Denote the solution trajectories of the time-invariant system

dx

dt= F (x) (3)

as x(t; x0, t0), which is the solution of equation (3) at time t starting from x0 at t0. We writex(·; x0, t0) for the set of all points lying along the trajectory.Definition 3 (! limit set). The ! limit set of a trajectory x(·; x0, t0) is the set of all points z " Rn

such that there exists a strictly increasing sequence of times tn such that

s(tn; x0, t0) # z

as n # $.

5

c

c

Example 3. Consider the linear system

dx1

dt= !ax1

dx2

dt= !bx1 ! cx2.

with a, b, c > 0, for which we have

A =

!

!a 0!b !c

"

P =

!

p11 p12

p21 p22

"

.

We choose Q = !I " R2!2 and the corresponding Lyapunov equation is

!

!a !b

0 !c

" !

p11 p12

p21 p22

"

+

!

p11 p12

p21 p22

" !

!a 0!b !c

"

=

!

1 00 1

"

and solving for the elements of P yields

P =

#

b2+ac+c2

2a2c+2ac2"b

2c(a+c)"b

2c(a+c)12

$

or

V (x) =b2 + ac + c2

2a2c + 2ac2x2

1 !b

c(a + c)x1x2 +

1

2x2

2.

It is easy to verify that P > 0 (check its eigenvalues) and by construction P = !I < 0. Hence thesystem is asymptotically stable.

4 Krasolvskii-Lasalle Invariance Principle (optional)

The Krasolvskii-Lasalle invariance principle provides a way to prove asymptotic stability when V

is negative semi-definite (which is usually much easier to find).

Denote the solution trajectories of the time-invariant system

dx

dt= F (x) (3)

as x(t; x0, t0), which is the solution of equation (3) at time t starting from x0 at t0. We writex(·; x0, t0) for the set of all points lying along the trajectory.Definition 3 (! limit set). The ! limit set of a trajectory x(·; x0, t0) is the set of all points z " Rn

such that there exists a strictly increasing sequence of times tn such that

s(tn; x0, t0) # z

as n # $.

5

Verify that P > 0

Page 11: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

• A is Hermitian (or symmetric in the case of real matrices) matrix is positive definite if:

- All the diagonal entries are positive - Each diagonal entry is greater than the sum of the

absolute values of all other entries in the same row.

11

How to determine positive-definiteness

Sufficient but not necessary!

Page 12: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

• A is Hermitian (or symmetric in the case of real matrices) matrix is positive definite if and only if:

- M is positive-definite if and only if all the following matrices have a positive determinant:

- the upper left 1-by-1 corner of M, - the upper left 2-by-2 corner of M, - ... - M itself.

- All the eigenvalues of M are positive.

12

Necessary and sufficient criteriaSylvester’s criterion

Page 13: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

Definition (! limit set). The ! limit set of a trajectory x(· ; x0, t0) is the set ofall points z 2 R such that there exists a strictly increasing sequence of time tnthat satisfies

limn!1

tn =1

and as n !1x(tn; x0, t0) = z

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x1 = 4x2 � x1�x21 + x

22 � 4

x2 = �4x1 � x2�x21 + x

22 � 4

�<latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">AAACdXicfZHNSiNBFIUrPepo+5eZWYpQGBVFot1NQDdCwI3LCEYFO7bVleqkSPUPVbclocnr+Q6+w2xn3Ik3sRcaxQsFH+fWqcs9FWZKGnCcp4r1Y25+4efikr28srq2Xv31+8qkueaizVOV6puQGaFkItogQYmbTAsWh0pch4OzSf/6QWgj0+QSRpnoxKyXyEhyBigF1Xu/m0IxDNzx7mljGHh1ROorEcEe0p13gNqdV2/4Wvb6sO/7dmnw0FBHh4sO7xtHUK05h8606GdwS6iRslpB9QUn8DwWCXDFjLl1nQw6BdMguRJj28+NyBgfsJ64RUxYLEynmCYxpjuodGmUajwJ0Kn63lGw2JhRHOLNmEHfzPYm4pe9yX6yO5wZD9FJp5BJloNI+Nv0KFcUUjrJmnalFhzUCIFxLXEByvtMMw74Ix+e53E4jWts2xiYOxvPZ7jyDl3ki0at2SijWyQbZIvsEZcckyY5Jy3SJpw8kr/kH/lfebY2rW1r9+2qVSk9f8iHso5eAYd6vd8=</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">AAACdXicfZHNSiNBFIUrPepo+5eZWYpQGBVFot1NQDdCwI3LCEYFO7bVleqkSPUPVbclocnr+Q6+w2xn3Ik3sRcaxQsFH+fWqcs9FWZKGnCcp4r1Y25+4efikr28srq2Xv31+8qkueaizVOV6puQGaFkItogQYmbTAsWh0pch4OzSf/6QWgj0+QSRpnoxKyXyEhyBigF1Xu/m0IxDNzx7mljGHh1ROorEcEe0p13gNqdV2/4Wvb6sO/7dmnw0FBHh4sO7xtHUK05h8606GdwS6iRslpB9QUn8DwWCXDFjLl1nQw6BdMguRJj28+NyBgfsJ64RUxYLEynmCYxpjuodGmUajwJ0Kn63lGw2JhRHOLNmEHfzPYm4pe9yX6yO5wZD9FJp5BJloNI+Nv0KFcUUjrJmnalFhzUCIFxLXEByvtMMw74Ix+e53E4jWts2xiYOxvPZ7jyDl3ki0at2SijWyQbZIvsEZcckyY5Jy3SJpw8kr/kH/lfebY2rW1r9+2qVSk9f8iHso5eAYd6vd8=</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit>

x1 = x2

x2 = �x1<latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit>

x1 = x2

x2 = � sin x1 � 0.5x2<latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit>

Page 14: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

x1 = 4x2 � x1�x21 + x

22 � 4

x2 = �4x1 � x2�x21 + x

22 � 4

�<latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit><latexit sha1_base64="X8dI3zyxSAEaW5DVrt7CJGD57IY=">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</latexit>

x1 = x2

x2 = �x1<latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit><latexit sha1_base64="IgCscotfUUmtUuF1uz3l/H9N6cE=">AAACNXicbZDLSsNAFIYn9VbjLerSzWBR3FiSUtCNUHDjsoK9QBvCZDpph04uzJxIS+jWp3GrPosLd+LWNxCnbRa29cCBn+/cOL+fCK7Att+Nwtr6xuZWcdvc2d3bP7AOj5oqTiVlDRqLWLZ9opjgEWsAB8HaiWQk9AVr+cPbab31yKTicfQA44S5IelHPOCUgEaehbu9GLKR50zOb0Zepds1c1DR4FJzzyrZZXsWeFU4uSihPOqe9aM30DRkEVBBlOo4dgJuRiRwKtjE7KaKJYQOSZ91tIxIyJSbzT6Z4DNNejiIpc4I8Iz+nchIqNQ49HVnSGCglmtT+G9NsAB4b7R0HoJrN+NRkgKL6Px6kAoMMZ56hXtcMgpirAWhkusHMB0QSShoRxfW09CXvD+AiWlqw5xle1ZFs1J2tL6vlmrV3LoiOkGn6AI56ArV0B2qowai6Ak9oxf0arwZH8an8TVvLRj5zDFaCOP7F0MWqyo=</latexit>

x1 = x2

x2 = � sin x1 � 0.5x2<latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">AAACRXicbZDNSsNAFIUn9a/Gv6pLN4NFcWNJiqIbQXDjsoLVQhPCZDpph04mYeZGWkJew6dxqz6DD+FOXKrTmoVWLwwcvnPnXu4JU8E1OM6LVZmbX1hcqi7bK6tr6xu1za0bnWSKsjZNRKI6IdFMcMnawEGwTqoYiUPBbsPhxcS/vWNK80Rewzhlfkz6kkecEjAoqDleL4F8FLjF/tkoaHqeXYKmAYee5nJq4kPsNI6xwUGt7jScaeG/wi1FHZXVCmofZiLNYiaBCqJ113VS8HOigFPBCtvLNEsJHZI+6xopScy0n08vK/CeIT0cJco8CXhKf/7ISaz1OA5NZ0xgoGe9CfzXEywC3hvNrIfo1M+5TDNgkn5vjzKBIcGT7HCPK0ZBjI0gVHFzAKYDoggFk/Cv8TQOFe8PoLBtE5g7G89fcdNsuEZfHdXPj8roqmgH7aID5KITdI4uUQu1EUX36AE9oifr2Xq13qz379aKVf7ZRr/K+vwChZ2wkQ==</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit><latexit sha1_base64="CuXvyGt5nQE0FFMe+dam2epzzMc=">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</latexit>

Definition (invariant set). The set M ⇢ Rn is said to be an invariant set if forall y 2 M and t0 � 0, we have

x(t; y , t0) 2 M for all t � t0.<latexit sha1_base64="Xcxwqq1erIhNgU38ru7ZdF57b+U=">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</latexit><latexit sha1_base64="Xcxwqq1erIhNgU38ru7ZdF57b+U=">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</latexit><latexit sha1_base64="Xcxwqq1erIhNgU38ru7ZdF57b+U=">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</latexit><latexit sha1_base64="Xcxwqq1erIhNgU38ru7ZdF57b+U=">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</latexit>

Page 15: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

Remarks:

• The word “largest” refers to the union of all invariant sets within S

• If r = , then the origin is globally asymptotically stable

15

Theorem (Krasovskii-Lasalle). Let V : Rn 7! R be a locally positive definitefunction such that, on the compact set ⌦r = {x 2 R : V (x) r}, we haveV (x) 0. Define

S = {x 2 ⌦r : V (x) = 0}.

As t ! 1, any trajectory starting inside ⌦r converges to the largest invariantset inside S. That is, the ! limit set of any such trajectory is contained insidethe largest infant set in S. In particular, if S contains no invariant set except theequilibrium xe = 0, then the origin is asymptotical stable.

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Page 16: Lecture 5 - how to find a Lyapunov function?€¦ · R. M. Murray Lyapunov Stability Analysis 17 October 2007 This lecture provides an overview of Lyapunov stability for time-invariant

Example

16

S = {(x1, x2) | x2 = 0}

Does not contain any invariant set, except x=0

d

dt

x1

x2

�=

x2

gl sinx1 � k

mx2