Một số định lý điểm bất động đối với các phép co cyclic - Pdf 29

ϕ
ϕ
ϕ
ϕ
ϕ
ϕ
ϕ
φ
φ
φ
φ
ϕ
ϕ
0
ϕ ϕ
ϕ
ϕ
ϕ
ϕ ϕ ϕ
0 0
ϕ
ϕ
ϕ
ϕ
ϕ
0 0
ϕ
ϕ
X d : X × X → R
X
d(x, y) ≥ 0 x, y ∈ X d (x, y) = 0 x = y

→ x lim
n→∞
x
n
= x
d (x, x
n
) → 0 n → ∞
(X, d)
{x
n
} ⊂ X x
n
→ x x
n
→ y x = y
{x
n
}, {y
n
} X x
n
→ x, y
n
→ y d (x
n
, y
n
) →
d (x, y)


) = x

f
f F
f
X p : X ×X → [0, +∞)
p (x, y) = p (y, x)
p (x, x) = p (x, y) = p (y, y) x = y
p (x, x) ≤ p (x, y)
p (x, z) ≤ p (x, y) + p (y, z) − p (y, y)
x, y, z ∈ X
(X, p)
p X τ
p
X
{B
p
(x, ε) : x ∈ X, ε > 0} B
p
(x, ε) = {y ∈
X : p (x, y) < p (x, x) + ε} x ∈ X ε > 0
(X, p)
{x
n
} ⊂ X x ∈ X
lim
n→∞
p(x, x
n

0
, δ)) ⊂ B
p
(f(x
0
), )
f : X → X X f
x ∈ X
(X, p)
{x
n
} (X, p) 0
lim
n,m→∞
p(x
n
, x
m
) = 0
(X, p) 0 0
X τ
p
x ∈ X
p(x, x) = 0
(X, p) {x
n
} ⊂ X
x
n
→ x ∈ X p(x, x) = 0 lim

X
i
X
i
= φ i = 1, . . . , m
f (X
1
) ⊂ X
2
, f (X
2
) ⊂ X
3
, . . . , f (X
m−1
) ⊂ X
m
, f (X
m
) ⊂ X
1
ϕ : R
+
→ R
+
ϕ
ϕ t
1
, t
2

, , A
m
, A
m+1
X
A
1
= A
m+1
Y =
m

i=1
A
i
f : Y → Y
{A
i
}
m
i=1
Y f
ϕ : R
+
→ R
+
d (f (x) , f (y)) ≤ ϕ (d (x, y)) (1.1)
x ∈ A
i
y ∈ A

→ R
+
(c)
ϕ
ϕ (t) < t t ∈ R
+
ϕ


k=0
ϕ
k
(t) t ∈ R
+
ϕ : R
+
→ R
+
(c)
s : R
+
→ R
+
s (t) =


k=0
ϕ
k
(t), t ∈ R

0
∈ X F : X → X
F : X → X
d(F (x), F (y)) < d(x, y) x, y ∈ X x = y.
{x
n
} X x
1
= F (x
0
), x
2
= F (x
1
), . . . , x
n
= F (x
n−1
) =
F
n
(x
0
), . . .
X F : X → X
X x ∈ X {F
n
(x)}
X F
(X, d) m

i=1
A
i
x
0
∈ Y
{x
n
}
n≥0
x

d(x
n
, x

) ≤ s(ϕ
n
(d(x
0
, x
1
))), n ≥ 1.
(2.1)
d(x
n
, x

) ≤ s(ϕ
n

n
, x
n+1
) = d (f (x
n−1
) , f (x
n
)) , n ≥ 1. (2.4)
x
n
= f (x
n−1
) n ≥ 1
n ≥ 0 i
n
∈ {1, 2, , m}
x
n
∈ A
i
n
x
n+1
∈ A
i
n+1
d (x
n
, x
n+1

(d (x
0
, x
1
)) . (2.6)
n ≥ 0 s
n
=
n

k=0
ϕ
k
(d (x
0
, x
1
))
d (x
n
, x
n+p
) ≤ s
n+p−1
− s
n−1
. (2.7)
ϕ d (x
0
, x

i=1
A
i
lim
n→∞
x
n
= p ∈ Y
m

i=1
A
i
Y f
i = 1, . . . , m {x
n
}
n≥0
A
i
i = 1, . . . , m A
i
{x
i
n
k
}
{x
n
} {x

:
m

i=1
A
i

m

i=1
A
i
.
ϕ (c) f ϕ
d (f (x) , f (y)) ≤ ϕ (d (x, y)) < d (x, y) x, y ∈
m

i=1
A
i
.
x


m

i=1
A
i
f

i
0
+1
d (f (x) , f (x

)) ≤ ϕ (d (x, x

)) .
ϕ
d (f
n
(x) , x

) ≤ ϕ
n
(d (x, x

)) n ≥ 0. (2.8)
ϕ x = x

f
n
(x) → x

n → ∞ x ∈ Y
x

f
n ≥ 1 p → ∞
n ≥ 0 k ≥ 1 ϕ f

n ≥ 0 k ≥ 2
d (x
n+k
, x
n+k+1
) ≤ ϕ
2
(d (x
n+k−2
, x
n+k−1
)) .
n ≥ 0 k ≥ 2
d (x
n+k
, x
n+k+1
) ≤ ϕ
n
(d (x
n
, x
n+1
)) (2.11).
d (x
n
, x
n+p
) ≤ d (x
n


k=0
ϕ
k
(d (x
n
, x
n+1
)). (2.13)
s
x ∈ Y n = 0
x
0
= x
d (x, x

) ≤


k=0
ϕ
k
(d (x, f (x))) = s (d (x, f (x))) . 
f : Y → Y


n=0
d

f

, x
1
)) .


n=0
d

f
n
(x
0
) , f
n+1
(x
0
)




n=0
ϕ
n
(d (x
0
, x
1
)) = s (d (x
0


∈ Y f(x

) = x

f ϕ
x ∈ Y d (f (x) , f (x

)) ≤ ϕ (d (x, x

))
ϕ n ≥ 0
d (f
n
(x) , x

) ≤ ϕ
n
(d (x, x

)) .


n=0
d (f
n
(x) , x

) ≤


n → ∞ F
f
= {x

}
f : Y → Y
x

∈ Y f(x

) = x

n ∈ N z
n
∈ Y
d (z
n
, f (z
n
)) → 0, n → ∞. (2.14)
z
n
n ∈ N
d (z
n
, x

) ≤ s (d (z
n
, f (z

n
(x)) → 0 n → ∞
f : Y → Y
x

∈ Y f(x

) = x

n ∈ N z
n
∈ Y
d (z
n
, f (z
n
)) → 0, n → ∞. (2.16)
n ≥ 0
d (z
n+1
, x

) ≤ d (z
n+1
, f (z
n
)) + d (f (z
n
) , f (x



) ≤ d (z
n+1
, f (z
n
)) + ϕ (d (z
n
, x

)) . (2.18)
n ≥ 1
d (z
n
, x

) ≤ d (z
n
, f (z
n−1
)) + ϕ (d (z
n−1
, x

)) .
ϕ
d (z
n+1
, x

) ≤ d (z

1
, f (z
0
))) + ϕ
n+1
(d (z
0
, x

)) .
(2.19)
ϕ b
n
= d (z
n+1
, f (z
n
))
d (z
n+1
, f (z
n
))+ϕ (d (z
n
, f (z
n−1
)))+ +ϕ
n
(d (z
1

, x

) + d (x

, f
n
(x)) (2.21)
n → ∞
d (z
n+1
, f
n
(x)) → 0 n → ∞.
f 
f : Y → Y
g : Y → Y
g x

g
∈ F
g
η > 0
d (f (x) , g (x)) ≤ η x ∈ X. (2.22)
d

x

f
, x


d

x

g
, f

x

g

= s

d

g

x

g

, f

x

g

.
s
d

n → ∞ F
f
= {x

}
{f
n
}
n≥0
f
n ∈ N η
n
∈ R
+
η
n
→ 0 n → ∞
d (f
n
(x) , f (x)) ≤ η
n
x ∈ Y.
f f
n
x

x

n
n ∈ N

i=1
Y f
d (x, y) ≤ ρ (x, y) x, y ∈ Y
(Y, d)
f : (Y, d) → (Y, d)
f : (Y, ρ) → (Y, ρ) ϕ ϕ : R
+
→ R
+
(c)
F
f
= {x

}
{f
n
(x
0
)}
n≥0
x

∈ (Y, d) x
0
∈ X
x
0
∈ Y
{f

t = 0
(X, d)
f : X → X X f
(X, d) m
A
1
, A
2
, , A
m
X A
m+1
= A
1
Y =
m

i=1
A
i
f : Y → Y Y Y ϕ
{A
i
}
m
i=1
Y f
ϕ : [0, ∞) → [0, ∞)
ϕ (t) > 0 t ∈ (0, ∞) ϕ (0) = 0
d (f(x), f(y)) ≤ d (x, y) − ϕ (d (x, y)) (3.1)

ϕ : [0, ∞) → [0, ∞) ϕ (t) =
t
2
t ∈ [0, +∞) ϕ
|f(x) − f(y)| = | −
x
3
− (−
y
3
)| =
1
3
|x − y|

1
2
|x − y| = |x − y| −
1
2
|x − y|
= |x − y| − ϕ(|x − y|).
f ϕ
X = R
A
1
= A
2
= = A
m

|
≤ |x − y| −
|x − y|
2
|x − y| + 2
.
f ϕ
(X, d) m
A
1
, A
2
, , A
m
X Y =
m

i=1
A
i
f ϕ f
z ∈
m

i=1
A
i
x
0
∈ Y =

)) ≤ d (x
n
, x
n+1
) − ϕ (d (x
n
, x
n+1
)) .
t
n
= d (x
n
, x
n+1
)
t
n+1
≤ t
n
− ϕ (t
n
) ≤ t
n
(3.2)
{t
n
} {t
n
}

n+p
≤ t
n
−pϕ (L)
p ∈ N p L = 0
ε > 0 N
0
∈ N d (x
N
0
, x
N
0
+1
) ≤ min

ε
2
, ϕ

ε
2

f B (x
N
0
, ε)
x ∈ B (x
N
0

N
0
)
<
ε
2
+
ε
2
= ε. (3.3)
d (x, x
N
0
) >
ε
2
ε
2
< d (x, x
N
0
) ≤ ε.
ϕ ϕ (t) > 0 ϕ

ε
2

≤ ϕ (d (x, x
N
0

ε
2

+ ϕ

ε
2

≤ ε.
f(x) ∈ B (x
N
0
, ε) f
B (x
N
0
, ε) x
n
∈ B (x
N
0
, ε)
n > N
0
{x
n
} Y
B (x
N
0

i
m

i=1
A
i
= φ.
Z =
m

i=1
A
i
Z
f Z f
|Z
: Z → Z
f
|Z
f
|Z
z ∈ Z x
0
x ∈ Y
z ∈ Z =
m

i=1
A
i

, A
2
, , A
m
X Y =
m

i=1
A
i
{A
i
}
m
i=1
Y f
d (x, y) ≤ ρ (x, y) x, y ∈ Y
(Y, d)
f : (Y, d) → (Y, ρ)
f : (Y, d) → (Y, ρ) ϕ ϕ : [0, ∞) →
[0, ∞) ϕ(t) > 0
t > 0 ϕ (0) = 0
{f
n
(x
0
)} z ∈ Y (Y, d)
x
0
∈ Y z f

)} f(z) (Y, d)
f(z) = z z
f
z 


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