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³] n ¬°¥¿¾ã¼Æ. §ÚÌ·Qn©w¸q nºû(¼Ú¤ó)ªÅ¶¡©M¨ä¤¤ªº¦V¶q.
§Ú̥ͬ¡ªº¸gÅç¶È¤Îºû¼Æ¤£¶W¹L3ªºªÅ¶¡. ¦b°ª¤¤½Ò¥»¤¤,
2 ºû©M 3 ºûªº¦V¶q¥»¬O¥Î´X¦óªº¤èªk©w¸qªº.
·í¤Þ¤J®y¼Ð¶b«á, ¨CÓ2ºûªÅ¶¡ªºÂI¦³¨âÓ®y¼Ð,
¨CÓ 2 ºû¦V¶q¦³¨âÓ¤À¶q, ¦Ó¨CÓ 3 ºûªÅ¶¡ªºÂI¦³¤TÓ®y¼Ð,
¨CÓ 3 ºû¦V¶q¦³¤TÓ¤À¶q.
¦]¬° 2 ©Î 3 ºûªÅ¶¡ªºÂI§¹¥þ¥Ñ¨ä®y¼Ð¨M©w, ¦Ó¦V¶q¤]§¹¥þ¥Ñ¨ä¤À¶q¨M©w,
±q¥N¼ÆªºÆ[ÂI, µL½×®y¼Ð¤]¦n, ¤À¶q¤]¦n, ³£¥u¬O¹ê¼Æ¹ï©Î¤T¹ê¼Æ²Õ,
¥»½è¤W¨S¦³¤°»ò¤£¦P; ¦ý²Õ¦¨ÂIªº®y¼Ð©Î¦V¶qªº¤À¶q«á, §êºt¤£¦Pªº¨¤¦â¦Ó¤w.
¦b°ª¤¤½Ò¥»ÁÙ¦³¤@ÓÆ[©À¥i¨Ñ§Ú̧Q¥Î, ¨º«K¬O
¯x°}.
§ÚÌ¥Î
ªí¥Ü©Ò¦³¹ê¼Æªº¶°¦X,
ªí¥Ü©Ò¦³¹ê¼Æ
¯x°}ªº¶°¦X,
ºÙ¤§¬° n ºûªÅ¶¡ (n-dimensional space).
¤¤ªº¤¸¯À¤£¹L¬O n Ó¹ê¼Æ«ö¤@©wªº¦¸§Ç±Æ¦¨¤@¦C¦Ó¤w.
¥H¤U§Ṳ́À§O±q¦V¶qªºÆ[ÂI©MÂIªºÆ[ÂI¨Ó°Q½×
.
¦b°ª¤¤½Ò¥»¤¤´¿°Q½×¹L3ºû¦V¶qªººØºØ¹Bºâ. §ÚÌn§â³o¨ÇÆ[©À±À¼s¨ì n ºû
¥h. ³]
¤Î
¬°
¤¤ªº¨âÓ¤¸¯À.
.
¥O
«h x+y, cx, (c,x) ¤À§OºÙ¬° x »P y ªº©M, x ªº c ¿,
¤Î x »P y ªº¤º¿n (inner product).
ª`·N x+y ©M cx ªº©w¸q»P¯x°}ªº¥[ªk»P¿¼Æ©w¸q§¹¥þ¤@P.
¦]¬°¤º¿n (x,y) ¦³®É¤]¥Î
ªí¥Ü, ¦b^¤å¤¤¥¦¤]¥s dot product.
¤Tºû¦V¶qªÅ¶¡¤¤³o¨Ç¹Bºâ©Òº¡¨¬ªºªk«h,
¦b n ºû¦V¶qªÅ¶¡¤¤³£¤´µM¦¨¥ßŪªÌ¸Õ¦Û¦æÃÒ¤§.
·í§Ú̦b
¤¤¦Ò¼{³o¨Ç¹Bºâ®É,
¥¦«K¥s§@ n ºû¦V¶qªÅ¶¡(n-dimensional vector space),
¨ä¤¤ªº¤¸¯À¥s§@ n ºû¦V¶q. Y
,
«h¹ê¼Æ
¥s§@¥¦ªº¤À¶q (components).
¨CÓ¤À¶q³£¬O 0 ªº¦V¶q¥s§@¹s¦V¶q (null vector), §Ṳ́]¥Î 0 ªí¥Ü¥¦.
Y x ¬° n ºû¦V¶q«h (x,x) ªº¥¤è®Ú¥s§@¥¦ªºªø (magnitude,norm),
¥H
©Î |x| ªí¥Ü. Y¹G¦V¶q¤§ªø¬° 1, «hºÙ¸Ó¦V¶q¬°³æ¦ì (unit) ¦V¶q.
Y ,«h
¬°»P x ¦P¤è¦V¤§³æ¦ì¦V¶q.
¤¤ªº³æ¦ì¦V¶q u ³£¥i¥Hªí§@
¤§§Î, ¦¡¤¤
¬° u ©M x ¶bªº§¨¨¤. Y u ¬°
¤¤ªº³æ¦ì¦V¶q,
¥O ,
,
¬° u ©M¤T®y¼Ð¶b¶¡ªº§¨¨¤,
«h u ¦b¤T®yÀY¼Ð¶b¤Wªº§ë¼v¤À§O¬°
,
,
.
³o¤TӼƥs°µ u ªº¤è¦V¾l©¶ (directional cosines) ¦Ó u ¥i¥Hªí¦¨
¨ä¦¸§Ú̱qÂIªºÃö©À¨Ó¬Ý Rn. ¦b2ºû©Î3ºûªÅ¶¡¤¤,
ÂI¤]¬O¥Î 2 ©Î 3 Ó¹ê¼Æ (§Y¨ä®y¼Ð) ªí¥Üªº.
±À¼s¨ì°ªºû±¡§Î, §Ṳ́]§â n ºû¹ê¼Æ¦ê¬Ý¦¨ÂI.
³o¨ÇÂI©Òºc¦¨ªº¶°¦XºÙ¬° n ºûªÅ¶¡, ¤´¥Î
ªí¥Ü.
³]
¬°¤@ÂI. ¦pªG§â x ¬Ý¦¨ n ºû¦V¶q,
«KºÙ¤§¬°¸Ó®y¼Ð¦V¶q (coordinate vector).
®y¼Ð¦V¶q¬° 0 ªºÂI¥s°µ Rn ªºìÂI.
³] A, B ¬°¨âÂI, ¨ä®y¼Ð¦V¶q¤À§O¬° x, y.
«h y-x ¥ç¥Nªí¥H A ¬°°_ÂI, ¥H B ¬°²×ÂIªº¦V¶q,
¦³®É¥Î
¨Óªí¥Ü.
A, B ¤§¶¡ªº¶ZÂ÷©w¬° ,
³q±`¥H AB ªí¥Ü.
¦b n ºûªÅ¶¡¤¤¦P®É¦Ò¼{³o¶ZÂ÷®É, ¥¦«K§@ n ºû¼Ú¤óªÅ¶¡ (Eulidean space).
ÁöµM n ºûªÅ¶¡©M n ºû¼Ú¤óªÅ¶¡¦bÃö©À¤W¤£¤@¼Ë,
¦ý¬Ý¦¨¶°¦X®É¥¦Ì³£¬O n ºûªÅ¶¡ªº¤£¦P±¦V.
§â
¬Ý¦¨¦V¶qªÅ¶¡, «h¥¦ªº¤¸¯À x, y ¶¡«h¦³ x+y, x-y,
µ¥¹Bºâ, ¤S¦³¦V¶qªºªøªº·§©À.
§â
¬Ý¦¨¼Ú¤óªÅ¶¡, «h¥i¥H°Q½×
¤ºÂI¶¡ªº¶ZÂ÷,
¦ýÂI©MÂI¤£¯à°µ¥[ªk, ´îªkµ¥¹Bºâ. ¦]¬°§ÚÌ©T·N§â²Å¸¹²V¥Î,
©Ò¥HY x, y ¬°
¤ºªº¨âÓÂI, a, b ¬°¨âÓ¹ê¼Æ,
«h ax+by ¥i¥H¥Nªí¥H ax+by ¬°®y¼Ð¦V¶qªºÂI.
¥H«á§Ú̱`±`³o¼Ë¥Î.
¨Ò¦p¦b©³¤U°Q½×½u¬q©Mª½½u®É´Nn¦p¦¹¸ÑÄÀ¦b 2 ºû 3 ºûªÅ¶¡, ¤º¿n»P§¨¨¤.
§ë¼v¦³±K¤ÁÃö«Y, °ª¤¤½Òµ{¤w¦³¤¶²Ð, ¨änÂI¦p¤U:
³] A ©M B ¬°
¤º¨âÂI, ¨ä®y¼Ð¦V¶q¤À§O¬° x ©M y.
«h¶°¦X
ªí¥Ü½u¬q AB,
¦Ó¶°¦X
·í
®Éªí¥Ü³s±µ AB ªºª½½u.
°²Y A ©M B ³£¤£¬OìÂI O(§Y
,
¥O
ªí¥Ü OA ©M OB ªº§¨¨¤, «h
¦Ó OA ¦b OB ¤Wªº§ë¼v¬°
¥O D ¬°¥H
¬°®y¼Ð¦V¶qªºÂI.
D §Y A ¦b OB ¤Wªº§ë¼v,
¬O OB ©M A ¶ZÂ÷³Ìµuªº¦a¤è.
·í
®É, ¤£¦A¯à¯u¥¿¹Ï¥Ü
,
¥i¬O³o¨Ç´X¦ó«ä¸ô¨ÌµMºZ³q,
½Ð¬Ý¤U±ªº»¡©ú:
³] A, B ¬O
¤º¤GÂI, ¨ä®y¼Ð¦V¶q¤À§O¬° X ©M Y. ¥O
¤U¤å¤¤§Ú̱NÃÒ©ú L(t) ¬O³sµ² A, B ¤GÂIªº¦±½u¤¤ªø«×³Ìµuªº,
¦Ó¥B L(t) ªºªøè¦n¬O A ©M B ªº¶ZÂ÷ (¨£
¨Ò 12).
ÁÙ¥iÃÒ©ú
¤¤¥ô·NÂI C ªº®y¼Ð¦V¶q¬O§_¦b L(t) ¤W,
ºÝµø AC+CB=AB ¬O§_¦¨¥ß¦Ó©w(¨£²ßÃD 1).
¦]¦¹§Ú̧â AB ½u¬q©w°µ
.
Y ,
«h A, B ©Ò¨M©wªºª½½u¦ÛµM´N©w°µ
¤F
(°Ñ¬Ý²ßÃD2).
³o¼Ë©w¸q§¹¥þ²Å¦X§Ú̹ï½u¬q©Mª½½uªºª½Æ[»{ÃÑ,
¤£¥u¬O§Î¦¡¤W©M
±¡§ÎÃþ¦ü¦Ó¤w.
¦A°²©w A ©M B ³£¤£¬OìÂI (§Y
),
§ë¼vªº°ÝÃD¬Û·í©ó§ä OB ª½½u¤W©M A ³Ì±µªñªºÂI.
³] OB ½u¤W¥ô¤@ÂI¬°
,
«h
©M A ªº¶ZÂ÷¬°
.
¦p¤U¥Î²³æªº¥N¼Æpºâ´N¥i¨M©w
ªº³Ì¤pÈ©Ò¦b. ¦]
ÅãµM·í
®É,
¨ú±o³Ì¤pÈ.
³] D ¬°¥H
¬°®y¼Ð¦V¶qªºÂI.
D ºÙ¬° A ¦b OB ¤Wªº§ë¼v(projection),
¦Ó OD ºÙ¬° OA ¦b OB ¤Wªº§ë¼v;
¤]¥i¥H»¡
¬° x ¦b y ¤è¦Vªº§ë¼v.
¤S¦¹®É
¬G¦³¤£µ¥¦¡
³o«K¬O¦³¦Wªº Cauchy ¤£µ¥¦¡. ¦b³o¤£µ¥¦¡¤¤µ¥¸¹¦¨¥ßªº¥Rn±ø¥óÅãµM¬O
²{¦b¨ú
,
¨Ï
«h OA ¦b OB ¤Wªº§ë¼v¬°
¦p¦¹
¥iµø¬° OA ©M OB ªº§¨¨¤. °²¦p
,
§Y(x,y)=0, «hºÙ x ©M y ««ª½
(per-pendicular) ©Î¥¿¥æ (orthogonal).
¬°¤F¤è«K°_¨£, §ÚÌ»{¬°¹s¦V¶q©M©Ò¦³¦V¶q³£««ª½.
Y
¬°
¤¤ªº¦V¶q,
«h»P u ¦P¤è¦Vªº³æ¦ì¦V¶q
ªº½Ñ¤À¦V¶q«K¬O
u ©M½Ñ®y¼Ð¶b¶¡§¨¨¤ªº¾l©¶, §Ṳ́´ºÙ¤§¬° u ªº¤è¦V¾l©¶.
¥H¤W§Ú̦b
¤¤¤Þ¶i½u¬q¡Bª½½u¡B§¨¨¤¡B§ë¼vµ¥Æ[©À,
¤£¥u¾A¦Xì¨Ó
ªº¤½¦¡, ¦Ó¥B©M
¤¤ªºª½Æ[§¹¥þ¬Û®e.
Cauchy ¤£µ¥¦¡¬O¤W±pºâ¤¤³Ì«nªºµ²ªG, §Ú̯S¦a±N¥¦¥Î©w²zªº§Î¦¡ªí¥X:
¤U±ªº©w²z¬O¥j¨åªº²¦¤ó©w²z (Pythagoras theorem) ªº±À¼s, ½ÐŪªÌ¦Û¤vÃÒ©ú.
¥H¤U´XÓµ²ªG³£¥i±q Cauchy ¤£µ¥¦¡±o¨ì:
ÃÒ©ú. ±q Cauchy ¤£µ¥¦¡±o
¨âÃä¶}¤è, «K¥i±o¨ì©Ò¨Dªº¤£µ¥¦¡.
Yµ¥¸¹¦¨¤§, «h
,
±q¦Ó©Î x=0, ©Î¦³¤@¥¿¹ê¼Æ
¦b,
¨Ï
.
¤Ï¤§Y¦¹±ø¥ó¦¨¥ß, «h©öÃÒ¤£µ¥¦¡¤¤µ¥¸¹¦¨¥ß.
³o¤£µ¥¦¡«K¥s°µ¤T¨¤§Î¤£µ¥¦¡ (triangle inequality). §Q¥Î¥¦, §Ú̥ߧY±o¨ì
¦b¥»©w²z¤¤©Ò¦CÁ|ªº¶ZÂ÷ªº¤Tөʽ褤, ¤þ¤]¥s°µ¤T¨¤§Î¤£µ¥¦¡.
³o¼Ë±o¨ìªº¶ZÂ÷©M§Ú̪ºª½Æ[«D±`±µªñ.
¦]¦¹§ÚÌ»{¬°
¤¤¶ZÂ÷ªºÆ[©À¬O 2 ¤Î 3 ºûªÅ¶¡¤¤¶ZÂ÷Æ[©Àªº¦ÛµM±À¼s.
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1999-06-27