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X =
X
11
X
12
X
21
X
22
,
X
11
(n × n) X
22
(m × m)
X
11
6= 0
X
−1
=
X
−1
11
+ X
−1
11
X
12
H
−1
X
21
X
−1
11
−X
−1
11
X
12
H
−1
−H
−1
X
21
X
−1
11
H
−1
,
H = X
22
− X
21
X
−1
11
X
12
.
X
22
6= 0
X
−1
=
K
−1
−K
−1
X
12
X
−1
22
−X
−1
22
X
21
K
−1
X
−1
22
+ X
−1
22
X
21
K
−1
X
12
X
−1
22
,
K = X
11
− X
12
X
−1
22
X
21
.
X
11
6= 0 X
22
6= 0
X
−1
=
K
−1
−X
−1
11
X
12
H
−1
−H
−1
X
21
X
−1
11
H
−1
,
K H

X =
X
11
X
12
X
21
X
22
,
X
11
(n × n) X
22
(m × m)
X
11
X
H = X
22
− X
21
X
−1
11
X
12
X = X
11
H .
X
22
X
K = X
11
− X
12
X
−1
22
X
21
X = X
22
K .
X
11
= X
T
11
X
21
= X
T
12
X
22
= X
T
22
X > 0 ;
X
11
> 0 , X
22
− X
T
12
X
−1
11
X
12
> 0 ;
X
22
> 0 , X
11
− X
12
X
−1
22
X
T
12
> 0 .
X =
X
11
X
12
X
T
12
X
22
,
X
11
X
22
X
11
> 0 X ≥ 0
X
22
− X
T
12
X
−1
11
X
12
≥ 0 .
X
22
> 0 X ≥ 0
X
11
− X
12
X
−1
22
X
T
12
≥ 0 .
X =
X
11
X
12
X
13
X
T
12
X
22
X
23
X
T
13
X
T
23
X
33
.
X
22
> 0 X > 0
X
11
X
13
X
T
13
X
33
−
X
12
X
T
23
X
−1
22
(X
T
12
X
23
) > 0 .

X
x = (x
1
, x
2
, x
3
)
x
T
Xx = (x
2
+ X
−1
22
X
T
12
x
1
+ X
−1
22
X
23
x
3
)
T
X
22
(x
2
+ X
−1
22
X
T
12
x
1
+ X
−1
22
X
23
x
3
)+
+x
T
1
(X
11
− X
12
X
−1
22
X
T
12
)x
1
+ x
T
3
(X
33
− X
T
23
X
−1
22
X
23
)x
3
+
+2x
T
1
(X
13
− X
12
X
−1
22
X
23
)x
3
.
X
22
> 0 X > 0
X
11
− X
12
X
−1
22
X
T
12
X
13
− X
12
X
−1
22
X
23
X
T
13
− X
T
23
X
−1
22
X
T
12
X
33
− X
T
23
X
−1
22
X
23
> 0 ,
A n × n R r × r
X Y n × r r × n
A + XRY
(A + XRY )
−1
= A
−1
− A
−1
X(R
−1
+ Y A
−1
X)
−1
Y A
−1
.
A (m × n) r
A = (U
1
U
2
)
Σ 0
0 0
V
∗
1
V
∗
2
= U
1
ΣV
∗
1
,
∗
Σ = (σ
1
, ···, σ
r
) , σ
1
≥ ··· ≥ σ
r
> 0 ,
σ
i
= λ
1/2
i
(AA
∗
) A U = (U
1
U
2
) V =
(V
1
V
2
) U
∗
U = I V
∗
V = I
R(A) = (U
1
) , N(A
∗
) = (U
2
) ,
R(A
∗
) = (V
1
) , N(A) = (V
2
) ,
R(·) N(·)
(·)

X
11
= X
T
11
> 0 Y
11
= Y
T
11
> 0 (n × n)
X
12
X
22
= X
T
22
(n×k)
(k × k)
X =
X
11
X
12
X
T
12
X
22
> 0 ,
X
11
X
12
X
T
12
X
22
−1
=
Y
11
Y
12
Y
T
12
Y
22
Y
12
Y
22
X
11
I
I Y
11
≥ 0 , (I − X
11
Y
11
) ≤ k .
X
11
Y
11
+ X
12
Y
T
12
= I ,
X
11
Y
12
+ X
12
Y
22
= 0 ,
X
T
12
Y
11
+ X
22
Y
T
12
= 0 ,
X
T
12
Y
12
+ X
22
Y
T
22
= I .
I − X
11
Y
11
= X
12
Y
T
12
.
k
k
(I − X
11
Y
11
) ≤ k .
Y
11
= X
−1
11
(I − X
12
Y
T
12
)
X
T
12
X
−1
11
+ (X
22
− X
T
12
X
−1
11
X
12
)Y
T
12
= 0 .
Y
12
Y
12
X
T
12
X
−1
11
+ Y
12
(X
22
− X
T
12
X
−1
11
X
12
)Y
T
12
= 0 .
Y
12
X
T
12
= I − Y
11
X
11
.