Tomluoc6-MayHoc

8/7/2019 Tomluoc6-MayHoc

1/11

1

H C MY1 Gi i thi u h c myHai ph n tr c gi i thi u nh ng n i dung gi i quy t bi ton trn my tnh b ng phphp tm ki m v bi u di n tri th c trn my tnh b ng logic tnh ton. V i nh ng cngtrn, my tnh tr thnh cng c c l c h tr con ng i gi i quy t nhi u v n thTuy nhin, vi c gi i quy t nh ng v n v n cn i h i nh ng can thi p c a con ngc n pht bi u nh ng bi ton v d ng tm ki m ho c d i d ng logic tr c khi s d ntnh lm cng c gi i quy t. Vi c pht bi u tri th c cho v n thng th ng i h i chl n ho c khng th th c hi n y . i m kh khn ny xu t pht t ngay trong b n chth c c a con ng i: con ng i v n v n cha hi u bi t y v cc lnh v c lin quamnh.

H c my l h ng ti p c n trong thay v con ng i ph i ch ra nh ng tri th c c n gi i quy t bi ton, my tnh s t ng rt trch tri th c ny m t cch t nh ng d c cung c p. H c my m ph ng qu trnh h c c a con ng i qua cc m c t n

n ph c t p: u tin my tnh ghi nh nh ng tr ng h p xu t hi n v cu i cngnh ng tr ng h p t ng qut cha t ng xu t hi n.Trong m t bi ton h c my, u vo l m t t p d li u hu n luy n bao g m cc m

li u. M i m u d li u bao g m m t t p gi tr ng v i cc thu c tnh. T p thu c tnhchia lm hai ph n: thu c tnh quan st v thu c tnh k t qu . M c tiu c a h c my ltm m t nh x t thu c tnh quan st vo thu c tnh k t qu (tm m i quan h gi a thu c tnh qst v thu c tnh k t qu )ng v i t p d li u hu n luy n. nh x ny s c p d ng lnh ng m u quan st m i rt ra k t qu tng ng.

B ng d i y trnh by m t v d c a h c my, bi ton d on vi c c chi tennis khng.

# Outlook Temperature Hudmidity Wind Target 1 Sunny Hot High Weak No2 Sunny Hot High Strong No3 Overcast Hot High Weak Yes4 Rain Mild High Weak Yes5 Rain Cool Normal Weak Yes6 Rain Cool Normal Strong No7 Overcast Cool Normal Strong Yes8 Sunny Mild High Weak No9 Sunny Cool Normal Weak Yes

10 Rain Mild Normal Weak Yes11 Sunny Mild Normal Strong Yes12 Overcast Mild High Strong Yes13 Overcast Hot Normal Weak Yes14 Rain Mild High Strong No

Trong bi ton ny, h c my s tm m t m i quan h gi a cc thu c tnh quan st:Outlook (quang c nh),Temperature(Nhi t ),Humidity( m),Wind (S c gi) v i thu c tnh k t


2/11

2

qu Target . K t qu ny s dng d on gi trTarget khi nh p vo thu c tnh quan st chocc m u m i v d :

# Outlook Temperature Hudmidity Wind Target 15 Sunny Mild Normal Strong ?16 Rain Cool High Strong ?

Vi c d on cho m u 15 c th tng i d dng, v m u ny c cc gi tr quatng t m u s 11 nn gi trTarget cng tng t lYes(tr ng h p h c my n gi n ghi nh ). Tuy nhin vi c d on cho m u 16 s kh khn hn v m u ny khng gi ngk m t trong nh ng m u bi t. y l tr ng h p t ng qut c a h c my g p nhtr ng h p cha t ng xu t hi n. Cc phng php h c my a ra nh m gi i quy t btrong tr ng h p t ng qut.

2 Thu t ton cy nh danh (ID3)

2.1 Cy quy t nh

M t s thu t ton h c my bi u di n m i quan h nhn qu d i d ng cy quy t nh.cy quy t nh, cc nt nhnh v nt g c i di n nh ng thu c tnh quan st cn nt ldi n thu c tnh quy t nh. Hnh bn d i bi u di n m t cy quy t nh cho bi tochitennis trn.

V i cy quy t nh, ta c th d on gi tr k t qu cho nh ng m u m i b ng cchcy quy t nh, b t u t nt g c. V i thu c tnh ghi trn nt g c, ta ki m tra gi tr

ng trong m u d li u v i theo nhnh tng ng. Qu trnh d on k t thc nt l hl p l i b c tng t t i cc nt nhnh trn ng i n nt l. V d v i m u s 16, Target c tnh theo cc b c nh sau:

- Ki m traOutlook , th y Outlook = Rain

- Ki m tra _______, th y ______________. V yTarget =____________.

M t cy quy t nh t t c n tho cc tnh ch t: y : cy quy t nh c n kh p v i m i tr ng h p trong t p hu n luy n.n gi n (nguyn t cdao c o Occam): cy cng n gi n th cng t ng qut (khngqu kh p v i d li u hu n luy n).

Outlook

Wind HumiditYes

Rain SunnyOvercast

Yes NoWeak Strong

Yes NoNormal High


3/11

3

2.2 Thu t ton ID3Thu t ton ID3 do Ross Quinlan xu t dng xy d ng nh ng cy quy t nh thotnh ch t trn. Thu t ton tun theo nguyn t cdao c o Occam xy d ng nh ng cy quy t nh b ng cch m i b c ki m tra, c g ng ch n thu c tnh (nt nhnh) n gi n nhxc nh n gi n c a thu c tnh, ID3 s d ng gi tr o l entropy thng tin (

lo n thng tin).V i m t thu c tnh cho tr c, m t t p d li u c chia thnhn t p con v i cc t lpi

tng ng (v d , v i thu c tnhTarget , t p d li u hu n luy n c chia thnh 2 t p conYes v ip0 = 9/14 v t p conNo v ip1=5/14). Khi , entropy c a t p d li u trn thu c tnh c ch n l:

V d , entropy c a t p d li u tennis theo thu c tnh k t qu l:

H = ____________________________________ = ____________________________________

Entropy o h n lo n c a m t t p. Entropy cng cao th h n lo n c a t p cao. T p d li u l hon ton ng nh t khi entropy = 0. V trong tr ng h p t p d li ul p, t p d li u hon ton h n lo n s c entropy = 1.

Thu t ton ID 3 : B t u v i nt g c,1. Ch n A thu c tnh quy t nh t t nh t chont k ti p2. Gn A l thu c tnh quy t nh chont 3. V i m i gi tr c a A, t o nhnh con m i c ant 4. Phn lo i cc m u hu n luy n cho cc nhnh5. N u cc m u hu n luy n trong m t nhnh c phn lo i hon ton ( ng nh t

lo i) th NGNG, ta c m t nt l. Ng c l i, l p v i cc nt nhnh m i.

Thu c tnh t t nh t y l thu c tnh c entropy trung bnh th p nh t theo thu c tnhqu . Entropy trung bnh c a m t thu c tnh b ngtrung bnh theo t l c a entropy cc nhnh:

p d ng thu t ton ID3 cho bi ton h cchi tennis: L p l n 1: Xt l n l t cc thu c tnh


4/11

4

HRain = ____________________________________________________________ HOvercast = ____________________________________________________________ HSunny = ____________________________________________________________ AE (Outlook) = _________________________________________________________

HMild = ____________________________________________________________ HCool = ____________________________________________________________ HHot = ____________________________________________________________ AE (Temperature) = ______________________________________________________

H = ____________________________________________________________ H = ____________________________________________________________ AE (Humidity) = ________________________________________________________

H = ____________________________________________________________ H = ____________________________________________________________ AE (Wind) =____________________________________________________________ So snh ta th y thu c tnh ______________ c entropy trung bnh th p nh t nn ch

thu c tnh ny lm nt g c.

Wind

Humidity

Tem erature

Outlook Rain SunnyOvercast

4 5 6 10 14


5/11

5

L p l n 2: xt nhnh ____________________

Xt cc thu c tnh Entropy trung bnh

Thu c tnh _____________ c entropy trung bnh th p nh t nn ch n lm nt nhnh.

L p l n 3: xt nhnh ____________________

Xt cc thu c tnh Entropy trung bnh


6/11

6

Thu c tnh _____________ c entropy trung bnh th p nh t nn ch n lm nt nhnh.

Cy quy t nh k t qu

Sau khi xy d ng cy, ta c th rt ra cc lu t tng ng b ng cch duy t cc i trn cy t nt g c n nt l, m i ng i ng v i m t lu t:

o L1:o

L2:o L3:o L4:o L5:

Lu : M t phin b n khc c a thu t ton ID3 s d ng Informatic Gain thay centropy ch n thu c tnh quy t nh. Cng th c tnh Informatic Gain nh sau:

Gain(A) = Entropy(S) Entropy(A)Trong : S l t p m u v A l m t thu c tnh. Entropy(S): h n lo n c a t p

Entropy(A): h n lo n trung bnh c a thu c tnh A (cch tnh nh trn)Nguyn t c th c hi n: tng t trn ngo i tr ______________________________

__________________________________________________________________________

3 Thu t ton h c quy n p (ILA)Thu t ton h c quy n p ILA a ra h ng ti p c n ng c l i so v i thu t ton ID3. Tton ID3, qu trnh rt tri th c t d li u c xu t pht t ccthu c tnh quan st c a t p


7/11

7

d li u. T vi c ki m tra trn cc thu c tnh quan st, ID3 ch n nh ng thu c tnh c cctr m chng chia t p hu n luy n thnh nh ng t p con m t cch t t nh t. Cc thu c tns c ch n rt ra lu t cho d li u.

Ng c l i, trong ILA, qu trnh h c xu t pht tcc thu c tnh quy t nh. ILA chia t pd li u hu n luy n thnh cc t p con r i nhau, m i t p con l m t phn l p d a trn t

tnh quy t nh. Ti p n ILA s xem xt trong t ng phn l p xem c thu c tnh no (hoh p thu c tnh no) c gi tr ch xu t hi n trong l p m khng xu t hi n trong ckhc hay khng. N u c, nh ng (t h p) thu c tnh v gi tr s c ch n lm c phn l p cho l p .

Thu t ton ILA

1. Chia t p m u thnh cc b ng con ng v i thu c tnh quy t nh2. V i m i b ng con3. V i m i t h p thu c tnh c th c (b t u v i s l ng = 1)4. Tm cc gi tr ch xu t hi n b ng con ny m khng xu t hi n cc b ng con kh5. (N u c nhi u t h p th ch n t h p c s l ng m u tin nhi u nh t)6. S d ng t h p thu c tnh, gi tr v a tm c t o lu t7. nh d u cc dng xt8. N u cn dng cha xt, l p l i b c 39. L p l i t b c 2 v i cc b ng cn l i

p d ng ILA cho b ng bi tontennis:1. Chia t p d li u ban u thnh 2 b ng con:

# Outlook Temperature Hudmidity Wind Target 3 Overcast Hot High Weak Yes4 Rain Mild High Weak Yes5 Rain Cool Normal Weak Yes7 Overcast Cool Normal Strong Yes9 Sunny Cool Normal Weak Yes10 Rain Mild Normal Weak Yes11 Sunny Mild Normal Strong Yes12 Overcast Mild High Strong Yes13 Overcast Hot Normal Weak Yes

# Outlook Temperature Hudmidity Wind Target 1 Sunny Hot High Weak No2 Sunny Hot High Strong No6 Rain Cool Normal Strong No8 Sunny Mild High Weak No14 Rain Mild High Strong No


8/11

8

2. V i b ng Yes: cc gi tr sau khng xu t hi n trong b ng No: T h p 1 thu c tnh:

o __________________, cc m u: __________________

Lu t L1: N u ___________________ th Target = Yes (xo cc m u___________) T h p 2 thu c tnh:

# Outlook Temperature Hudmidity Wind Target 4 Rain Mild High Weak Yes5 Rain Cool Normal Weak Yes9 Sunny Cool Normal Weak Yes10 Rain Mild Normal Weak Yes11 Sunny Mild Normal Strong Yes

o O = S T= C, m u: 9o

_______________, m u: ________ o _______________, m u: ________ o _______________, m u: ________ o _______________, m u: ________

Lu t L2: N u ________________ th Target = Yes (xo cc m u________)cn l i

o _______________, m u: ________ o

_______________, m u: ________ o _______________, m u: ________ o _______________, m u: ________

Lu t L3: N u ________________ th Target = Yes (xo cc m u________)V i b ng No:

T h p 1 thu c tnh: khng c T h p 2 thu c tnh:

o O = S

T= H, m u: 1, 2o ______________, m u: ___________ o ______________, m u: ___________ o ______________, m u: ___________

Lu t L4: N u ________________ th Target = Yes (xo cc m u________)cn l i


9/11

9

o ______________, m u: ___________

Lu t L5: N u ________________ th Target = Yes (xo cc m u________)

K t lu n: v y cc lu t phn l p l L1L5.

4 Thu t ton Nave Bayes

4.1 Ti p c n th ng k v Lu t BayesTrong cch ti p c n th ng k, l thuy t quy t nh c s d ng ch n gi tr k t xum u m i. Theo l thuy t quy t nh, khi m t m u m ix c cung c p, gi tr c a thu c tnhquy t nhy l gi tr yk sao cho xc su tP(y=yk |x) l l n nh t. V d trong bi tontennis,v i m u #16 ta c n xc nh hai gi tr xc su tP(Target=Yes|#16)v P(Target=No|#16)vch n phn l p ng v i gi tr l n nh t trong hai gi tr ny.

Gi tr P(y=yk |x) th ng kh tnh c (do ph i c r t r t nhi u m u hu n luy n mth x p x chnh xc). Cng th c Bayes gip a gi tr trn v d ng d tnh hn:

Gi tr P(x)l nh nhau i v i m i phn l p nn ta ch c n so snh t s c a phn s tM t l n n a, gi trP(x|y=yk ) (g i l phn b c a d li u trong phn l p) cng kh tnh ton.Gi nh c l p c i u ki n gi a cc thu c tnh (Nave) cho php ta tnh phn b xcc a m u d li u thng quaphn b xc su t c a t ng gi tr thu c tnh thnh ph n:

V d v i #16, ta c th tnh:P(#16| Target=Yes)= P(Outlook=Rain| Target=Yes)x P(Temp=Cool| Target=Yes)x

P(Humidity=High| Target=Yes)x P(Wind=Strong| Target=Yes)v tnh tng t cho m uP(#16| Target=No).

4.2 Thu t ton h c my Nave BayesThu t ton h c my Nave Bayes bi u di n nh x h c d i d ng m t t p cc gi tr phxc su t. Cc gi tr phn b xc xu t c tnh trong giai o n hu n luy n v c s xc nh gi tr quy t nh cho nh ng m u m i.

Thu t ton Nave Bayes

1. Hu n luy nTh ng k ( m) xc su t c a cc l p yk P(yk ) v cc gi tr phn b xc su t

P(Ai=vij|yk ). n gi n ta k hi uRAi(vij, yk ) l t l cc m u c thu c tnhAi = vij thu cphn l pyk :


10/11

10

2. S d ngV i m i m u m ix, tnh kh nngx ri vo cc phn l pyk

v ch n phn l p c gi trS l n nh t.S a l i Laplace:khi d li u t, m t trong nh ng gi tr R c th = 0 do b nhi u. NR = 0 cc th gi tr S tng ng cng = 0. trnh tr ng h p , php s a l i a ra nh m m b o cc gi tr xc su t lun > 0. S a l i Laplace th c hi n nh

Cc gi tr P v R sau khi s a l i c s d ng nh bnh th ng.

p d ng thu t ton Nave Bayes vo v dtennis, ta th c hi n cc b c sau:# Outlook Temperature Hudmidity Wind Target 1 Sunny Hot High Weak No2 Sunny Hot High Strong No3 Overcast Hot High Weak Yes4 Rain Mild High Weak Yes5 Rain Cool Normal Weak Yes6 Rain Cool Normal Strong No7 Overcast Cool Normal Strong Yes8 Sunny Mild High Weak No9 Sunny Cool Normal Weak Yes10 Rain Mild Normal Weak Yes11 Sunny Mild Normal Strong Yes12 Overcast Mild High Strong Yes13 Overcast Hot Normal Weak Yes

14 Rain Mild High Strong No Hu n luy n:

P(Yes) = 9/14 s a l i: P(Yes) = 10/16P(No) = _____ s a l i: P(No) = _____ R Overlook (Sunny, Yes) = 2/9, (s a l i) = 2 + 1/9 + 3 = 3/12R Overlook (Overcast, Yes) = ___, (s a l i) = ____________ =____


11/11

11

R Overlook (Rain, Yes) = ____________=_____ (s a l i)R Overlook (Sunny, No) = ____________=_____ (s a l i)R Overlook (Overcast, No) = ____________=_____ (s a l i)R Overlook (Rain, No) = ____________=_____ (s a l i)

R Temperature(s a l i)

Hot Mild Cool

Yes

No

R Humidity(s a l i)

Normal High

Yes

No

R Wind (s a l i)

Weak Strong

Yes

No

D on cho m u #16:

S(Yes) = ________________________________________________________________

S(No) = ________________________________________________________________

V y #16 thu c v l p ______________

Tomluoc6-MayHoc

Documents

Transcript of Tomluoc6-MayHoc