¤U¤@¶: FIELD
¤W¤@¶: Unique Factorization Domain
«e¤@¶: Unique factorization domain ªº°ò¥»©Ê½è
§Ú̱N§Q¥ÎÃþ¦ü±À¾É
[x] ¬O unique factorization domain
ªº¤èªk±À¾É·í R ¬O unique factorization domain ®É
R[
x] = {
anxn +
... +
a1x +
a0 |
ai R}
³oºØ¥H R ¬°«Y¼Æªº
polynomials ©Ò§Î¦¨ªº polynomial ring ¬O¤@Ó unique factorization
domain.
Y
f (x) R[x] ¥B f (x) 0, «h§ÚÌ¥i±N f (x) ¼g¦¨
f (x) = anxn + ... + a1x + a0, ¨ä¤¤ an 0. ¦p¦P«e±°Q½× F[x]
ªº±¡ªp§ÚÌ¥i¥H©w¸q
deg(f (x)) = n. §Q¥Î©M Lemma 7.2.2
¦P¼ËªºÃÒ©ú§ÚÌ¥i¥H±o¨ì: Y
f (x), g(x) R[x] ¥B¬Ò¤£¬° 0, «h
deg(f (x) . g(x)) = deg(f (x)) + deg(g(x)).
¥Dnªºì¦]¬O Lemma
7.2.2 ªºµý©ú¶È¥Î¨ì¨âÓ«D 0 ¤¸¯À¬Û¼¤£¬° 0 (§Y integral
domain) ªº©Ê½è, ¨Ã¨S¦³¥Î¨ì field ªº©Ê½è. §Q¥Î degree
ªº³oÓ¯S©Ê§ÚÌ°¨¤W¦³¥H¤Uªº©Ê½è.
Lemma 8.4.3
¥O
R ¬O¤@Ó integral domain.
- R[x] ¤]¬O¤@Ó integral domain.
- R[x] ¤¤ªº unit ´N¬O R ¤¤ªº unit.
- Y a R ¬O R ¤¤ªº irreducible element «h a ¬Ý¦¨¬O
R[x] ¤¤ªº¤¸¯À (§Y±`¼Æ¦h¶µ¦¡) ®É¤]¬O irreducible.
µý ©ú.
(1) Y
f (
x)
0 ¥B
g(
x)
0, °²³]
f (
x) ªº³Ì°ª¦¸¶µ«Y¼Æ¬O
an ¥B
g(
x) ªº³Ì°ª¦¸¶µ«Y¼Æ¬O
bm, «h
f (
x)
. g(
x)
ªº³Ì°ª¦¸¶µ«Y¼Æ¬O
an . bm. ¥Ñ©ó
an,
bm R, ¥B
an,
bm 0 §Q¥Î
R ¬O integral domain ª¾
an . bm 0.
¤]´N¬O»¡
f (
x)
. g(
x) ¤£¥i¯à¬° 0 ¦h¶µ¦¡.
(2) Y
f (x) R[x] ¬O R[x] ¤¤ªº unit, «h§Q¥Î¦s¦b
g(x) R[x]
º¡¨¬
f (x) . g(x) = 1 ª¾
deg(f (x)) + deg(g(x)) = 0 (ª`·N 1
¬O±`¼Æ¦h¶µ¦¡¬G degree ¬° 0). ¬G±o
deg(f (x)) = deg(g(x)) = 0.
´«¥y¸Ü»¡ f (x), g(x) ³£¬O±`¼Æ¦h¶µ¦¡, ¤]´N¬O»¡
f (x), g(x) R.
µM¦Ó¥Ñ°²³]
f (x) . g(x) = 1 ª¾ f (x) ¬O R ¤¤ªº unit.
(3) °²³] a R ¬O R ¤¤ªº irreducible element. ª`·N¥Ñ degree
ªº©Ê½èª¾Y g(x) ¬O f (x) ªº divisor (¥Ñ©ó¦s¦b
h(x) R[x] º¡¨¬
g(x) . h(x) = f (x)), «h
deg(g(x))deg(f (x)). ²Y±N a
¬Ý¦¨¬O±`¼Æ¦h¶µ¦¡, ¥Ñ©ó deg(a) = 0, ¬Gª¾¦b R[x] ¤¤ a ªº divisor
¨ä degree ¤]¬O 0. ´«¥y¸Ü»¡¦b R[x] ¤¤ a ªº divisor ³£¬O R
ªº¤¸¯À. ¬G§Q¥Î a ¦b R ¤¤¬O irreducible ª¾³o¨Ç divisor n¤£¬O R
¤¤ªº unit ´N¬O©M a associates. µM¦Ó¥Ñ (2) ª¾ R ¤¤ªº unit
·íµM¤]¬O R[x] ¤¤ªº unit, ¬Gª¾ a ¦b R[x] ¨ÌµM¬O irreducible.
·í R ¬O¤@Ó unique factorization domain ®É, ¥O F ¬° R ªº
quotient field. ±µ¤U¨Ó§ÚÌ·Q§Q¥Î R ©M F[x] ³£¬O unique
factorization domain (Theorem 7.2.14) ÃÒ©ú R[x] ¬O¤@Ó
unique factorization domain.
¬°¤F±N R[x] ©M F[x] ªºÃö«Y¬Û³sµ², §ÚÌÁÙ¬O±o¤¶²Ð©M
[x]
¤¤Ãþ¦üªº content ªº·§©À. º¥ý¥Ñ Proposition 8.4.1 ª¾Y
f (x) = anxn + ... a1x + a0 R[x], «h
an,..., a1, a0 ªº
greatest common divisor ¬O¦s¦bªº.
Definition 8.4.4
Y
f (
x) =
anxn +
... +
a1x +
a0 R[
x] ¥B
an,...,
a1,
a0 ªº
greatest common divisor ¬O
R ¤¤ªº unit, «hºÙ
f (
x) ¬O
R[
x] ¤¤ªº
primitive polynomial.
Lemma 8.4.5
°²³]
R ¬O¤@Ó unique factorization domain, «h¹ï¥ô·N
f (
x)
R[
x]
¥B
f (
x)
0, ³£¥i§ä¨ì
c R ¥B
f*(
x)
R[
x] ¬O
R[
x] ªº
primitive polynomial º¡¨¬
f (x) = c . f*(x).
¤S°²³]
f (x) |
= |
c . f*(x) |
|
|
= |
c' . g(x) |
|
¨ä¤¤
c,
c' R, ¥B
f*(
x),
g(
x)
R[
x] ¬O
R[
x] ªº primitive polynomials,
«h
c c' ¥B
f*(
x)
g(
x).
µý ©ú.
º¥ýÃÒ©ú¦s¦b©Ê: Y
f (
x) =
anxn +
... +
a1x +
a0, ¥O
c ¬°
an,...,
a1,
a0 ªº greatest common divisor. ©Ò¥H¹ï©Ò¦³ªº
i = 0, 1,...,
n ¬Ò¦³
ai =
c . bi, ¨ä¤¤
bi R, ¦Ó¥B
b0,...,
bn ªº greatest common divisor ¬O
R ªº unit. ¬G¥O
f*(
x) =
bnxn +
... +
b1x +
b0, «h
f*(
x) ¬O
R[
x] ªº primitive
polynomial ¥B
f (
x) =
c . f*(
x). ¬G±oÃÒ¦s¦b©Ê.
±µµÛÃÒ©ú°ß¤@©Ê: Y
f (x) = c' . g(x), ¨ä¤¤ g(x) ¬O R[x] ªº
primitive polynomial. °²³]
g(x) = an'xn + ... + a1'x + a0',
«h¹ï©Ò¦³
i = 0, 1,..., n, ¬Ò¦³
ai = c' . ai'. ´«¥y¸Ü»¡ c' ¬O
an,..., a0 ªº¤@Ó common divisor. ¦]¦¹¥Ñ c ¬O
an,..., a0
ªº greatest common divisor ª¾ c' | c. §Y¦s¦b d R ¨Ï±o
c = c' . d. §Q¥Î
ai = c . bi = c' . ai', §Ú̪¾¹ï©Ò¦³ªº
i = 0, 1,..., n, ¬Ò¦³
c' . (d . bi) = (c' . d ) . bi = c . bi = c' . ai'.
¨Ò¥Î
c' 0 ¥B
R ¬O integral domain,
¥i±o¹ï©Ò¦³ªº
i = 0, 1,...,
n, ¬Ò¦³
ai' =
d . bi. ´«¥y¸Ü»¡
d
¬O
an',...,
a0' ªº¤@Ó common divisor. µM¦Ó¥Ñ°²³]
an',...,
a0' ªº greatest common divisor ¬O unit, ¬G±o
d ¬O
R ªº¤@Ó unit. ´«¥y¸Ü»¡
c c'. ¦A§Q¥Î
f (
x) =
c . f*(
x) =
c' . g(
x), ¥H¤Î
R[
x] ¬O integral domain, ±o
d . f*(
x) =
g(
x). ¥Ñ©ó
d ¬O
R ªº unit ¤]¬O
R[
x] ªº unit, ¬G±o
f*(
x)
g(
x).
§Q¥Î Lemma 8.4.5 ªº°ß¤@©Ê, §Ú̦۵M¦³¥H¤Uªº©w¸q.
Definition 8.4.6
°²³]
R ¬O¤@Ó unique factorization domain. Y
f (
x)
R[
x]
¥i¼g¦¨
f (
x) =
c . f*(
x) ¨ä¤¤
c R ¥B
f*(
x) ¬O
R[
x] ªº
primitive polynomial, «hºÙ
c ¬°
f (
x) ªº
content, ©w¬°
c(
f ).
nª`·N¥Ñ Lemma 8.4.5 ªºÃÒ©ú§Ú̪¾¹D f (x) ªº content
¨ä¹ê´N¬O f (x) ©Ò¦³«Y¼Æªº greatest common divisor. ¥t¥ nª`·Nªº¬O
f (x) ªº content ¨ä¹ê¨Ã¤£¬O¤@Ó©T©wªºÈ, content ¤§¶¡·|®tÓ
associates.
§ÚÌ¥i¥H±N content ªº©w¸q±À¼s¨ì F[x]. §O§Ñ¤F F ¬O R ªº
quotient field, ©Ò¥H F ¤¤¨CÓ¤¸¯À³£¥i¥H¼g¦¨ a/b ªº§Î¦¡, ¨ä¤¤
a, b R ¥B b 0. ²¹ï¥ô·Nªº
f (x) = rnxn + ... + r1x + r0 F[x], ¥Ñ©ó¹ï¥ô·Nªº
i = 0, 1,..., n, ¬Ò¦³
ri = ai/bi, ¨ä¤¤
ai, bi R, §ÚÌ¥i§ä¨ì d R ¥B d 0 ¨Ï±o
d . f (x) R[x] (¤ñ¤è»¡¥O
d = bn ... b0). ¦]¦¹§Q¥Î Lemma 8.4.5
ª¾¦s¦b c R ¥H¤Î
f*(x) R[x] ¬O R[x] ªº primitive
polynomial ¨Ï±o
d . f (x) = c . f*(x). ¥Ñ©ó d 0, §ÚÌ¥i±N
f (x) ¼g¦¨
f (
x) =
. f*(
x).
´«¥y¸Ü»¡¥ô·N F[x] ¤¤«D 0 ªº
polynomial f (x) ¬Ò¥i¼g¦¨
f (x) = r . f*(x), ¨ä¤¤ r F ¥B
f*(x) R[x] ¬O R[x] ªº primitive polynomial. §Ų̵́MºÙ¦¹ r
¬O f (x) ªº content ¥B¤´°O§@ c(f ).
Corollary 8.4.7
°²³]
R ¬O¤@Ó unique factorization domain, ¥B
F ¬O
R ªº
quotient field. «h¹ï¥ô·N
f (
x)
F[
x] ¥B
f (
x)
0, ³£¥i§ä¨ì
c F ¥B
f*(
x)
R[
x] ¬O
R[
x] ªº primitive polynomial º¡¨¬
f (x) = c . f*(x).
¤S°²³]
f (x) |
= |
c . f*(x) |
|
|
= |
c' . g(x) |
|
¨ä¤¤
c,
c' F, ¥B
f*(
x),
g(
x)
R[
x] ¬O
R[
x] ªº primitive polynomials,
«h¦s¦b
u R ¬O
R ªº unit ¨Ï±o
c =
u . c' ¥B
u . f*(
x) =
g(
x).
µý ©ú.
«e±¤wÃÒ¦s¦b©Ê, §Ú̶ÈÃҰߤ@©Ê. §Ú̱N
c ©M
c' ¤À§O¼g¦¨
c =
a/
b
¥B
c' =
a'/
b', ¨ä¤¤
a,
a',
b,
b' R ¥B
b 0,
b' 0. ±N
f (
x) ¼¤W
b . b', §Ú̦³
(
b . b')
. f (
x)
R[
x] ¥B
(b . b') . f (x) |
= |
(a . b') . f*(x) |
|
|
= |
(a' . b) . g(x). |
|
¬JµM
(
b . b')
. f (
x)
R[
x] §ÚÌ¥i¥H±N
Lemma
8.4.5 ®M¥Î¦b
(
b . b')
. f (
x) ¤W, ¬Gª¾¦s¦b
u R ¬O
R ¤¤ªº unit º¡¨¬
a . b' =
u . (
a' . b). ¤]´N¬O»¡
c =
u . c'. ¦A§Q¥Î
c' 0 ¤Î
F[
x] ¬O integral domain ±o
u . f*(
x) =
g(
x).
©M
[x] ¤@¼Ëªºª¬ªp, §Ú̦³¥H¤Uªº Gauss Lemma ¨ÓÀ°§U§ÚÌpºâ¨âÓ
polynomials ¬Û¼«á¤§ content.
Lemma 8.4.8 (Gauss)
°²³]
R ¬O¤@Ó unique factorization domain. Y
f (
x),
g(
x)
R[
x]
¬O
R[
x] ¤¤ªº primitive polynomials, «h
f (
x)
. g(
x) ¨ÌµM¬O
R[
x] ¤¤ªº primitive polynomial.
µý ©ú.
§Ú̧Q¥Î©M Lemma
7.3.5 ¬Û¦Pªºµý©ú, ©Ò¥H¥uµ¹¤j²¤ªºµý©ú. °²³]
f (
x)
. g(
x) ¤£¬O primitive polynomial, ªí¥Ü
f (
x)
. g(
x)
©Ò¦³«Y¼Æªº greatest common divisor ¤£¬O
R ¤¤ªº unit. ¦]¦¹§Q¥Î
R
¬O unique factorization domain ª¾¦s¦b
p R ¬O
R ¤¤ªº¤@Ó
irreducible (¤]¬O prime) element ¬O
f (
x)
. g(
x) ©Ò¦³«Y¼Æªº
common divisor. µM¦Ó
f (
x) ©M
g(
x) ¬Ò¬O primitive polynomials,
p ¤£¥i¯à¾ã°£©Ò¦³
f (
x) ªº«Y¼Æ¤]¤£¥i¯à¾ã°£©Ò¦³
g(
x) ªº«Y¼Æ.
©Ò¥HY
i ¬O³Ì¤pªº¼Æ¨Ï±o
f (
x) ªº
xi ¶µ«Y¼Æ¤£¯à³Q
p ¾ã°£, ¦Ó
j ¬O³Ì¤pªº¼Æ¨Ï±o
g(
x) ªº
xj ¶µ«Y¼Æ¤£¯à³Q
p ¾ã°£,
«h«Ü®e©ö¬Ý¥X
f (
x)
. g(
x) ªº
xi + j ¶µ«Y¼Æ¤£¥i¯à³Q
p ¾ã°£.
³o©M
p ¬O
f (
x)
. g(
x) ¦U¶µ«Y¼Æªº common divisor ¥Ù¬Þ, ¬G±oÃÒ
f (
x)
. g(
x) ¬O
R[
x] ªº primitive polynomial.
Primitive polynomial ¦b R[x] ¤¤¬O©M F[x] ·¾³qªº¾ô¼Ù, ¨Æ¹ê¤W¦b
R[x] ¤¤¤£¬O±`¼Æªº irreducible element ³£¬O primitive polynomial.
Lemma 8.4.9
°²³]
R ¬O¤@Ó unique factorization domain. Y
f (
x)
R[
x] ¬O
R[
x] ªº irreducible element ¥B
deg(
f (
x))
1, «h
f (
x) ¬O
R[
x] ¤¤ªº primitive polynomial.
µý ©ú.
Y
f (
x) ¬O
R[
x] ¤¤ªº irreducible element, ¥Ñ©ó
f (
x) ¥i¼g¦¨
f (
x) =
c(
f )
. f*(
x) ¨ä¤¤
c(
f )
R R[
x] ¥B
f*(
x)
R[
x], ¬Gª¾
c(
f ) ¬O
f (
x) ªº¤@Ó divisor. ¥Ñ
f (
x) ¬O
irreducible element ªº°²³]ª¾
c(
f ) ¬O
R ¤¤ªº unit (
f (
x)
¤£¥i¯à©M
c(
f ) associates ¦]
deg(
f (
x))
1 ¦ý
deg(
c(
f )) = 0),
¬Gª¾
f (
x) ¬O primitive polynomial.
Y
f (x), g(x) R[x], ¥Ñ©ó
R F, f (x) ©M g(x)
¥i¦P®É¬Ý¦¨¬O R[x] ªº polynomials ¤]¥i¥H¬Ý¦¨¬O F[x] ªº
polynomials. ¦]¦¹³o¨âÓ polynomials
¶¡Ãö«Y¬Ý¦¨¬O R[x] ©Î F[x] ¤¤ªº±¡ªp´N·|¤£¦P. ¨Ò¦pY
g(x) = f (x) . h(x), ¨ä¤¤
h(x) R[x] §ÚÌ´N»¡
f (x) | g(x)
in R[x]. µM¦ÓY
h(x) F[x], §ÚÌ´N»¡
f (x) | g(x) in
F[x]. ¥Ñ©ó
R[x] F[x], «Ü¦ÛµMªº§Ú̪¾¹DY
f (x) | g(x) in R[x] «h
f (x) | g(x) in F[x]. µM¦Ó¤@¯ë¨Ó»¡
f (x) | g(x) in F[x] ¤£¨£±o·|¦³
f (x) | g(x) in R[x]. ¤£¹L·í f (x)
¬O R[x] ªº primitive polynomial ®É, ´N¹ï¤F.
Lemma 8.4.10
°²³]
R ¬O¤@Ó unique factorization domain ¥B
F ¬O
R ªº
quotient field. °²³]
f (
x),
g(
x)
R[
x] ¥B
f (
x) ¬O
R[
x] ªº¤@Ó
primitive polynomial, «h
f (
x) |
g(
x) in
F[
x] Y¥B°ßY
f (
x) |
g(
x) in
R[
x].
µý ©ú.
§ÚÌ¥unÃÒ©ú: Y
f (
x) |
g(
x) in
F[
x] «h
f (
x) |
g(
x) in
R[
x]. ¥Ñ°²³]ª¾¦s¦b
h(
x)
F[
x] ¨Ï±o
g(
x) =
f (
x)
. h(
x). §Q¥Î
content, §Ú̱o
c(g) . g*(x) = (c(f ) . c(h)) . (f*(x) . h*(x)).
¨ä¤¤
c(
g),
c(
f )
R ¬O
g(
x),
f (
x) ªº
content, ¦Ó
c(
h)
F ¬O
h(
x) ªº content, ¥B
g*(
x),
f*(
x)
¥H¤Î
h*(
x) ³£¬O
R[
x] ªº primitive polynomials. §Q¥Î Lemma
8.4.8 ª¾
f*(
x)
. h*(
x) ¬O
R[
x] ªº primitive
polynomial. ¦A§Q¥Î Corollary
8.4.7 ª¾¦s¦b
u R ¬O
R ªº
unit º¡¨¬
u . c(
g) =
c(
f )
. c(
h). µM¦Ó¥Ñ
f (
x) ¬O
R[
x] ªº
primitive polynomial, ª¾
c(
f ) ¬O
R ªº unit. ¤S¥Ñ°²³]
g(
x)
R[
x] ª¾
c(
g)
R. ¬G±o
c(
h) =
c(
f )
-1 . u . c(
g)
R.
µM¦Ó
h(
x) =
c(
h)
. h*(
x), ¬G¥Ñ
c(
h)
R ¥H¤Î
h*(
x)
R[
x]
¥i±o
h(
x)
R[
x]. ´«¥y¸Ü»¡
f (
x) |
g(
x) in
R[
x].
§Q¥Î Lemma 8.4.10 §ÚÌ¥i¥H±o¨ì R[x] ©M F[x] ¤¤ prime
element ªºÃö«Y.
Corollary 8.4.11
°²³]
R ¬O¤@Ó unique factorization domain ¥B
F ¬O
R ªº
quotient field ¥B°²³]
p(
x)
R[
x] ¬O
R[
x] ªº primitive
polynomial. Y
p(
x) ¬O
F[
x] ¤¤ªº prime element «h
p(
x) ¬O
R[
x] ¤¤ªº prime element.
µý ©ú.
°²³]
p(
x) ¬O
F[
x] ¤¤ªº prime element. nÃÒ©ú
p(
x) ¬O
R[
x]
¤¤ªº prime element, §ÚÌ¥²¶·ÃÒ©úY
p(
x) |
f (
x)
. g(
x) in
R[
x], ¨ä¤¤
f (
x),
g(
x)
R[
x], «h
p(
x) |
f (
x) in
R[
x] ©Î
p(
x) |
g(
x) in
R[
x]. ¦]
p(
x) ¬O
R[
x] ¤¤ªº primitive
polynomial, ¥Ñ Lemma
8.4.10 §Ú̦³
p(
x) |
f (
x)
. g(
x)
in
F[
x]. ¬G§Q¥Î
p(
x) ¬O
F[
x] ªº prime element, §Ú̪¾
p(
x) |
f (
x) in
F[
x] ©Î
p(
x) |
g(
x) in
F[
x]. ¦A¤@¦¸§Q¥Î
Lemma
8.4.10, §Ú̪¾
p(
x) |
f (
x) in
R[
x] ©Î
p(
x) |
g(
x) in
R[
x], ¬G±oÃÒ
p(
x) ¬O
R[
x] ªº prime element.
¥t¥ ¦b R[x] ©M F[x] ¤¤n°Ï¤À²M·¡ªº¬O¤@Ó R[x] ¤¤ªº polynomial
¦b R[x] ©M F[x] ¤¤¥i§_¤À¸Ñ (§Y¬O§_ irreducible) ªºÃöÁp©Ê.
Lemma 8.4.12
°²³]
R ¬O¤@Ó unique factorization domain ¥B
F ¬O
R ªº
quotient field ¥B°²³]
f (
x)
R[
x] ¤Î
deg(
f (
x))
1. Y¦s¦b
g(
x),
h(
x)
F[
x] º¡¨¬
deg(
g(
x))
1 ¥B
deg(
h(
x))
1,
¨Ï±o
f (
x) =
g(
x)
. h(
x), «h¦s¦b
m(
x),
n(
x)
R[
x] º¡¨¬
deg(
g(
x)) = deg(
m(
x)) ¥B
deg(
h(
x)) = deg(
n(
x)) ¨Ï±o
f (
x) =
m(
x)
. n(
x).
µý ©ú.
§Q¥Î content §Ú̱N
f (
x) =
g(
x)
. h(
x) ¼g¦¨:
c(f ) . f*(x) = (c(g) . c(h)) . (g*(x) . h*(x)),
¨ä¤¤
c(
f )
R,
c(
g),
c(
h)
F, ¦Ó
f*(
x),
g*(
x) ©M
h*(
x) ³£¬O
R[
x] ªº primitive polynomial. §Q¥Î Lemma
8.4.8 ª¾
g*(
x)
. h*(
x) ¬O
R[
x] ªº primitive polynomial, ¬G¥Ñ Lemma
8.4.5 ª¾¦s¦b
u R ¬O
R ªº unit ¨Ï±o
c(
g)
. c(
h) =
c(
f )
. u. ´«¨¥¤§,
c(
g)
. c(
h)
R. ¬GY¥O
m(
x) = (
c(
g)
. c(
h))
. g*(
x)
R[
x],
n(
x) =
h*(
x), «h
m(
x),
n(
x) ²Å¦X©w²z©Òn¨D.
¥Ñ Lemma 8.4.12 §ÚÌ¥i±o R[x] ©M F[x] ¶¡ irreducible
element ªºÃö«Y.
Corollary 8.4.13
°²³]
R ¬O¤@Ó unique factorization domain ¥B
F ¬O
R ªº
quotient field. Y
p(
x)
R[
x] º¡¨¬
deg(
p(
x))
1 ¬O
R[
x]
ªº primitive polynomial, «h
p(
x) ¬O
R[
x] ªº irreducible element
Y¥B°ßY
p(
x) ¬O
F[
x] ªº irreducible element.
µý ©ú.
º¥ý°²³]
p(
x) ¬O
R[
x] ªº irreducible element,
nÃÒ©ú
p(
x) ¤]¬O
F[
x] ªº irreducible element. °²¦p
p(
x) ¦b
F[
x] ¤£¬O irreducible element, «h¦s¦b
g(
x),
h(
x)
F[
x] º¡¨¬
deg(
g(
x))
1 ¥B
deg(
h(
x))
1 ¨Ï±o
p(
x) =
g(
x)
. h(
x).
¬G¥Ñ Lemma
8.4.12 ª¾¦s¦b
m(
x),
n(
x)
R[
x] º¡¨¬
deg(
m(
x))
1 ¥B
deg(
n(
x))
1 ¨Ï±o
p(
x) =
m(
x)
. n(
x).
´«¥y¸Ü»¡¥Ñ
1
deg(
m(
x)) < deg(
p(
x)) ª¾,
m(
x) ¬O
p(
x) ¦b
R[
x] ªº¤@Ó divisor ¥B¬J¤£¬O unit ¤]¤£©M
p(
x) associates. ¬Gª¾
p(
x) ¤£¬O
R[
x] ªº irreducible element. ¦¹©M°²³]¥Ù¬Þ, ¬Gª¾
p(
x)
¬O
F[
x] ªº irreducible element.
¤Ï¤§, °²³] p(x) ¬O F(x) ªº irreducible element. ¦pªG p(x) ¦b
R[x] ¤¤¤£¬O irreducible, §Y¦s¦b
l (x), m(x) R[x] º¡¨¬
p(x) = l (x) . m(x), ¨ä¤¤ l (x) ©M m(x) ³£¤£¬O R[x] ¤¤ªº
unit. ¦ý
l (x), m(x) R[x] F[x], ¬G§Q¥Î p(x) ¬O F[x]
¤¤ªº irreducible element ª¾ l (x) ©M m(x) ¤¤¥²¦³¤@Ó¬O F[x]
¤¤ªº unit (§Y±`¼Æ¦h¶µ¦¡). ´N°²³]¬O
l (x) = a R §a! ¥Ñ°²³]
a ¤£¯à¬O R ªº unit, §_«h l (x) = a ¬O R[x] ªº unit (Lemma
8.4.3). µM¦Ó¥Ñ
f (x) = l (x) . m(x) = a . m(x) ¥B
m(x) R[x] ª¾ a ¬O f (x) ¦U¶µ«Y¼Æ¤§ common divisor, §Y
a | c(f ) in
R. ¦ý¥Ñ°²³] f (x) ¬O primitive polynomial ª¾ c(f ) ¬O R ¤¤ªº
unit, ¬G¥Ñ
a | c(f ) in R ª¾ a ¬O R ªº unit; ¦¹©M a ¤£¬O
R ªº unit ¬Û¥Ù¬Þ. ¬Gª¾ f (x) ¦b R[x] ¤¤¬O irreducible.
±µµÛ§Ų́ӬÝÃÒ©ú R[x] ¬O unique factorization domain ³ÌÃöÁ䪺©Ê½è.
Proposition 8.4.14
°²³]
R ¬O¤@Ó unique factorization domain, «h
R[
x] ¤¤ªº
irreducible element ©M prime element ¬O¬Û¦Pªº.
µý ©ú.
¥Ñ©ó
R[
x] ¬O integral domain, §Ú̪¾
R[
x] ªº prime element ´N¬O
irreducible element (Lemma
8.1.8). ¦]¦¹¥unÃÒ©úY
f (
x)
R[
x] ¬O¤@Ó irreducible element, «h
f (
x) ¬O¤@Ó prime element.
§ÚÌ·QÂÇ¥Ñ
F[
x] (³o¸Ì
F ¬O
R ªº quotient field) ¤¤ªº
irreducible element ¬O prime element (Proposition
7.2.11)
¨ÓÃÒ©ú.
º¥ý¦Ò¼
deg(f (x)) = 0 (§Y
f (x) = a R ¬O±`¼Æ) ªº±¡§Î. ¦] a R ¬O irreducible ¥B R ¬O unique factorization domain, ¥Ñ
Proposition 8.4.2 ª¾ a ¬O R ªº prime element. §ÚÌnÃÒ©ú
a ¤]¬O R[x] ¤¤ªº prime element. °²³]
g(x), h(x) R[x] º¡¨¬
a | g(x) . h(x) in R[x], §Y¦s¦b
l (x) R[x] ¨Ï±o
a . l (x) = g(x) . h(x). §Q¥Î content ±o
(a . c(l )) . l*(x) = (c(g) . c(h)) . (g*(x) . h*(x)),
¨ä¤¤
c(
l ),
c(
g),
c(
h)
R ¥B
l*(
x),
g*(
x),
h*(
x)
R[
x] ¬O
R[
x] ªº
primitive polynomials. ¥Ñ Lemma
8.4.8 ª¾
g*(
x)
. h*(
x)
¨ÌµM¬O primitive polynomial, ¬G¥Ñ Lemma
8.4.5 ª¾¦s¦b
u R
¬O
R ªº unit º¡¨¬
u . a . c(l )= c(g) . c(h),
´«¥y¸Ü»¡
a |
c(
g)
. c(
h) in
R. §Q¥Î
a ¬O
R ªº prime element
¤§°²³]±o
a |
c(
g) ©Î
a |
c(
h). µM¦Ó
g(
x) =
c(
g)
. g*(
x),
¬GY
a |
c(
g) «h
a |
g(
x). ¦P²zY
a |
c(
h), «h
a |
h(
x). ¬Gª¾
a =
f (
x) ¬O
R[
x] ¤¤ªº prime element.
²¦Ò¼
deg(f (x))1 ªº±¡§Î. ¥O F ¬O R ªº quotient field.
¦]¬° f (x) ¬O R[x] ªº irreducible element ¥Ñ Corollary
8.4.13 ª¾ f (x) ¬O F[x] ªº irreducible element. µM¦Ó
Proposition 7.2.11 §i¶D§Ú̦¹®É f (x) ¤]¬O F[x] ¤¤ªº
prime element. ¥Ñ©ó Lemma 8.4.9 §i¶D§ÚÌ f (x) ¬O R[x]
ªº primitive polynomial, ¬G¥i®M¥Î Corollary 8.4.11 ±oÃÒ f (x)
¤]¬O R[x] ¤¤ªº prime element.
²¦b§Ú̦³¨¬°÷ªº©Ê½è¨ÓÀ°§U§ÚÌÃÒ©ú R[x] ¤]¬O¤@Ó unique
factorization domain. ¤j®a¥i¥Hªu¥ÎÃÒ©ú
[x] ¬O unique
factorization domain (Theorem 7.3.13) ªº¤èªk¨Ó³B²z.
³o¸Ì§ÚÌ·QÂÇ¥Ñ F[x] ¬O unique factorization domain (Theorem
7.2.14) ³oӨƹê¨Ó±À¾É. ³oÓÃÒ©ú¤£¨£ªº¤ñ¸û²©ú,
¤£¹L¥i¥HÀ°§U§Ú̦h¤F¸Ñ R[x] ©M F[x] ¶¡ªºÃöÁp.
Theorem 8.4.15
°²³]
R ¬O¤@Ó unique factorization domain, «h
R[
x] ¤]¬O¤@Ó
unique factorization domain.
µý ©ú.
¥O
F ¬O
R ªº quotient field.
º¥ýÃÒ©ú¦s¦b©Ê: §Y¥ô¤@ R[x] ¤¤«D 0 ¥B¤£¬O unit ªº¤¸¯À f (x)
¥i¼g¦¨¦³¦hÓ R[x] ªº irreducible elements ªº¼¿n. º¥ý±N f (x)
¼g¦¨
f (x) = c(f ) . f*(x), ¨ä¤¤ c(f ) R ¥B
f*(x) R[x]
¬O R[x] ªº primitive polynomial. Y c(f ) ¤£¬O unit, «h§Q¥Î R
¬O unique factorization domain §ÚÌ¥i¥H±N c(f ) ¼g¦¨¦³¦hÓ R
¤¤ªº irreducible elements ªº¼¿n. §Q¥Î Lemma 8.4.3 (3) ª¾¹D
c(f ) ¥i¥H¼g¦¨¦³¦hÓ R[x] ¤¤ªº irreducible elements ªº¼¿n.
©Ò¥H§ÚÌ¥unÃÒ©ú f*(x) ¥i¥H¼g¦¨¦³¦hÓ irreducible elements
ªº¼¿n. ²±N f*(x) ¬Ý¦¨¬O F[x] ¤¤ªº¤¸¯À, «h§Q¥Î F[x] ¬O
unique factorization domain, ª¾¹D
f*(x) = p1(x) ... pm(x), ¨ä¤¤
p1(x),..., pm(x) F[x] ¬O F[x] ¤¤ªº irreducible elements.
¦A§Q¥Î content, ª¾¨CÓ pi(x) ³£¥i¼g¦¨
pi(x) = c(pi) . pi*(x), ¨ä¤¤
pi*(x) R[x] ¬O R[x] ªº primitive
polynomial. ´«¥y¸Ü»¡
f*(x) = (c(p1) ... c(pm)) . p1*(x) ... pm*(x).
§Q¥Î Lemma
8.4.8 ª¾
p1*(
x)
... pm*(
x) ¬O
R[
x] ªº primitive polynomial, ¬G¥Ñ
f*(
x) ¬O
R[
x]
ªº primitive polynomial ¥H¤Î Lemma
8.4.5 ª¾
c(
p1)
... c(
pm) =
u ¬O
R ¤¤ªº unit, ¥Ñ Lemma
8.4.3 ª¾
u ¤]¬O
R[
x]
ªº unit. ¦]¦¹§ÚÌ¥unÃÒ©ú
p1*(
x),...
pm*(
x) ¬O
R[
x] ¤¤ªº
irreducible elements ´N¥i. ¦p¦¹¤@¨Ó
f*(x) = (u . p1*(x)) . p2*(x) ... pm*(x),
©Ò¥H
f*(
x) ¥i¥H¼g¦¨¦³¦hÓ
irreducible elements ªº¼¿n (ª`·N
u . p1*(
x) ©M
p1*(
x)
associates, ©Ò¥H¤]¬O
R[
x] ¤¤ªº irreducible element). µM¦Ó¦]
pi(
x) =
c(
pi)
. pi*(
x), ¥Ñ
pi(
x) ¦b
F[
x] ¤¤ irreducible
ª¾
pi*(
x) ¤]¬O
F[
x] ªº irreducible element. ¥Ñ©ó
pi*(
x) ¬O
R[
x] ªº primitive polynomial, ®M¥Î Corollary
8.4.13 ª¾
pi*(
x) ¤]¬O
R[
x] ªº irreducible element.
±µµÛÃÒ©ú¤À¸Ñªº°ß¤@©Ê: ¨ä¹ê§ÚÌ¥i¥H§Q¥Î Proposition 8.4.14
ª½±µÃÒ©ú°ß¤@©Ê, ¤£¹L³o¸Ì§Ų̵́M§Q¥Î F[x] ©M R ¬O unique
factorization domain ¨ÓÃÒ©ú. º¥ý°²³]
f (x) |
= |
(a1n1 ... arnr) . p1nr + 1(x) ... pvnr + v(x) |
|
|
= |
(b1m1 ... bsms) . q1ms + 1(x) ... qwms + w(x), |
|
¨ä¤¤
a1,...
ar R (§Y
deg(
ai) = 0) ¬O
R[
x] ¤¤¨â¨â¤£ associates ªº irreducible elements ¦Ó
p1(
x),...,
pv(
x)
R[
x] ¬O
R[
x] ¤¤¨â¨â¤£ associates ¥B degree ¤j©ó 0 ªº
irreducible elements, ¹ï©ó
b1,...,
bs R ¥H¤Î
q1(
x),...,
qw(
x)
R[
x] ¤]¬O¦P¼Ëªº°²³]. º¥ýª`·N¥Ñ©ó³o¨Ç
pi(
x) ©M
qj(
x) ³£¬O
R[
x] ¤¤ªº irreducible elements ¥B
deg(
pi(
x))
1 ¥H¤Î
deg(
qj(
x))
1, ¥Ñ Lemma
8.4.9 ª¾³o¨Ç
pi(
x)
©M
qj(
x) ³£¬O primitive polynomial, ¬G¥Ñ Lemma
8.4.8 ¥H¤Î
Lemma
8.4.5 ª¾¦s¦b
R ¤¤ªº unit
u º¡¨¬
a1n1 ... arnr = u . b1m1 ... bsms,
¬G§Q¥Î
R ¬O unique
factorization domain ªº©Ê½èª¾¸g¹L¾A·í¶¶§Ç±¼´«§Ú̦³
r =
s,
ai bi ¥B
ni =
mi,
i = 1,...,
r. ©Ò¥H³Ì«á§ÚÌ¥un¦Ò¼
f0(x) |
= |
u . p1nr + 1(x) ... pvnr + v(x) |
|
|
= |
q1ms + 1(x) ... qwms + w(x) |
|
³o¤@³¡¤Àªº°ß¤@©Ê. ¥Ñ©ó
f0(
x)
R[
x]
F[
x], ¥B
pi(
x),
qi(
x) ¬O
R[
x] ¤¤ªº irreducible elements ©Ò¥H¤]¬O
F[
x]
¤¤ªº irreducible elements (Corollary
8.4.13), ¬G§Q¥Î
F[
x] ¬O
unique factorization domain ª¾¸g¹L«±Æ«á
v =
w,
pi(
x) =
ki . qi(
x) ¥B
ni =
mi,
i =
r + 1,...
r +
v, ¨ä¤¤
ki F.
µM¦Ó
pi(
x) ©M
qi(
x) ³£¬O
R[
x] ªº primitive polynomial, ¬Gª¾
ki ¬O
R ªº unit. ´«¨¥¤§, ¹ï©Ò¦³ªº
i =
r + 1,...,
r +
v, ¬Ò¦³
pi(
x)
qi(
x). ¬G±oÃҰߤ@©Ê.
³Ì«á§ÚÌ¨Ó¬Ý Theorem 8.4.15 ¤@Ó«nªºÀ³¥Î. Y R ¬O¤@Ó
unique factorization domain, ¥Ñ Theorem 8.4.15 ª¾ R' = R[x]
¤]¬O¤@Ó unique factorization domain. ²¦Ò¼ R'[y] ³o¤@Ó¥H y
¬°ÅÜ¼Æ R' ªº¤¸¯À¬°«Y¼Æªº polynomial ring, ¤]´N¬O R'[y]
ªº¤¸¯À³£¬O
fn(x)yn + fn - 1(x)yn - 1 + ... + f1(x)y + f0(x),
¨ä¤¤¹ï©Ò¦³ªº
i = 0, 1,..., n,
fi(x) R' = R[x] ¬O«Y¼Æ¦b R ªº
x ªº¦h¶µ¦¡. «Ü®e©ö¬Ý¥X
R'[y] = R[x][y] = R[x, y] ´N¬O¥H R
ªº¤¸¯À¬°«Y¼Æ x, y ¬°Åܼƪº¨âÓÅܼƪº¦h¶µ¦¡©Ò¦¨ªº¶°¦X, ¬G¦A¦¸¥Ñ
Theorem 8.4.15 ª¾ R[x, y] ¬O unique factorization domain.
§ÚÌ¥i¥H±N¥H¤Wªº½×z±À¼s¨ì
R[x1,..., xn] ³oÓ¥H R
ªº¤¸¯À¬°«Y¼Æ
x1,..., xn ¬°Åܼƪº n ÓÅܼƪº polynomial ring:
Theorem 8.4.16
°²³]
R ¬O¤@Ó unique factorization domain, «h
R[
x1,...,
xn]
³oÓ
n ÓÅܼƪº polynomial ring ¤]¬O¤@Ó unique factorization
domain.
µý ©ú.
§Q¥Î¼Æ¾ÇÂk¯Çªk, ·í
n = 1 ®É Theorem
8.4.15 §i¶D§ÚÌ
R[
x1]
¬O¤@Ó integral domain. °²³]
n - 1 ®É,
R' =
R[
x1,...,
xn - 1] ¬O
unique factorization domain. ¦A¥Ñ Theorem
8.4.15 ª¾
R'[
xn] =
R[
x1,...,
xn] ¤]¬O unique factorization domain.
Theorem 8.4.16 ¬O¤@Ó¥N¼Æ¤W«Ü«nªº©w²z, ³Ì±`¨£ªºª¬ªp¬O·í
F ¬O¤@Ó field ®É¦] F[x1] ¬O¤@Ó unique factorization domain,
¬Gª¾
F[x1,..., xn] ¤]¬O¤@Ó unique factorization domain.
¤U¤@¶: FIELD
¤W¤@¶: Unique Factorization Domain
«e¤@¶: Unique factorization domain ªº°ò¥»©Ê½è
Administrator
2005-06-18