The stiffness matrix associated with the unstable swing is
S=10-100100-10100001
S
1
0
-1
0
0
1
0
0
-1
0
1
0
0
0
0
1
-
Find the three distinct eigenvalues,
λ1=1
λ1
1
,
λ2=2
λ2
2
,
λ3=0
λ3
0
,
along with their associated eigenvectors
e
1
,
1
e
1
,
1
,
e
1
,
2
e
1
,
2
,
e
1
,
3
e
1
,
3
,
e
3
,
1
e
3
,
1
, and projection matrices,
P1
P1,
P2
P2,
P3
P3.
What are the respective geometric multiplicities?
-
Use the folk theorem that states "in order to transform a matrix
it suffices to transform its eigenvalues" to arrive at a guess for
S1/2
S
12
.
Show that your guess indeed satisfies
S1/2S1/2=S
S
12
S
12
S
.
Does your
S1/2
S
12
have anything in common with the element-wise square root of
SS?
-
Show that
ℝP3=ℕS
P3
S
.
-
Assemble
S+=1λ1P1+1λ2P2
S+
1
λ1
P1
1
λ2
P2
and check your result against
pinv(S) in Matlab.
-
Use
S+S+ to solve
Sx=f
S
x
f
where
f=0102T
f
0
1
0
2
and carefully draw before and after pictures of the unloaded
and loaded swing.
-
It can be very useful to sketch each of the eigenvectors in
this fashion. In fact, a movie is the way to go. Please run the Matlab
truss demo by typing
truss and view all 12 of the movies.
Please sketch the 4 eigenvectors of (1) by showing how they
deform the swing.