ung dung mang neural trong nhan dang ki tu 4538

8/3/2019 Ung Dung Mang Neural Trong Nhan Dang Ki Tu 4538

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n tt nghip ng dng mng neural trong nhn dng k t

LI CM N

Em xin chn thnh cm n cc thy, cc c khoa Cng ngh Thng tin

Trng i hc Dn lp Hi Phng tn tnh dy d, truyn t cho chng emnhiu kin thc qu bu.

Em xin t lng bit n su sc n thy Th.s Ng Trng Giang, ngi

tn tnh gip v truyn t nhiu kinh nghim ti c th c thc hin

v hon thnh.

Xin chn thnh cm n cc bn trong khoa Cng Ngh Thng Tin, i Hc

Dn Lp Hi Phng gip , ng vin ti rt nhiu trong qu trnh thc hin

ti.

Em xin trn thnh cm n!

Hi Phng, thng 07 nm 2007.Sinh vin

Bi Quang Chin

Bi Quang Chin Trang 1


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MC LC

LI CM N......................................................................................................1

MC LC............................................................................................................2

LI NI U......................................................................................................3

CHNG 1:

TNG QUAN V MNG NEURAL NHN TO .............................................4

CHNG 2:

NG DNG MNG NEURAL NHN DNG K T ....................................27

CHNG 3:

CI T CHNG TRNH TH NGHIM ...................................................40

KT LUN........................................................................................................71

TI LIU THAM KHO..................................................................................73



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LI NI U

Ngy nay khng ai c th ph nhn vai tr cc k quan trng ca my tnh

trong nghin cu khoa hc k thut cng nh trong i sng. My tnh lmc nhng iu k diu v gii c nhng vn tng chng nan gii. Cng

ngy cng c nhiu ngi t hi, liu my tnh c kh nng suy ngh nh con

ngi hay cha? Chng ta s khng tr li cu hi y. Thay vo , chng ta s

nu ra nhng khc bit ch yu gia cch lm vic ca my tnh v b c con

ngi.

Mt my tnh, d c mnh n u chng na, u phi lm vic theo mt

chng trnh chnh xc c hoch nh trc bi cc chuyn gia. Bi ton

cng phc tp th vic lp trnh cng cng phu. Trong khi con ngi lm vic

bng cch hc tp v rn luyn, khi lm vic con ngi c kh nng lin tng,

kt ni s vic ny vi s vic khc, v quan trng hn ht, h c th sng to.

Do c kh nng lin tng, con ngi c th d dng lm nhiu iu m

vic lp trnh cho my tnh i hi rt nhiu cng sc. Chng hn nh vic nhn

dng hay tr chi ch. Mt em b c th t hc hi nhn dng v phn loi

vt chung quanh mnh, bit c ci g l thc n, ci g l chi. Mt

ngi bnh thng cng c th on c vi ch trong mt ch. Nhng tht

kh m dy cho my tnh lm c nhng vic y. T lu cc nh khoa hc

nhn thy nhng u im ca b c con ngi v tm cch bt chc thc

hin trn nhng my tnh, to cho n c kh nng hc tp, nhn dng v phn

loi. Cc mng neural nhn to ra i t nhng n lc . N thc s c

ch v nhanh chng tr thnh mt hng nghin cu y trin vng trong mc

ch xy dng cc my thng minh tin gn ti tr tu con ngi. c bit l

lnh vc nhn dng.

Trong n ny s trnh by ng dng mng neural trong nhn dng k

t. Ni dung bo co gm nhng chng sau:

Chng 1:Tng quan v mng neural nhn to.

Chng 2: ng dng mng neural nhn dng k t.

Chng 3: Ci t chng trnh th nghim.



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CHNG 1:TNG QUAN V MNG NEURAL NHN TO

1.1. Khi nim mng neural .1.1.1. Tm hiu v Neural.

1.1.1.1. Neural sinh hc:

Mt neural c cu gm nhng thnh phn chnh sau: Dendrite, Soma,

Synapse, Axon nh hnh 1.1.

Hnh 1.1: M hnh neural sinh hc

Soma l thn ca neural.

Cc dendrites l cc dy mnh, di, gn lin vi soma, chng truyn d liu

(di dng xung in th) n cho soma x l. Bn trong soma cc d liu

c tng hp li, c th xem gn ng s tng hp y nh l mt php ly tng

tt c cc d liu m neural nhn c.Mt loi dy dn tn hiu khc cng gn vi soma l cc axon. Khc vi

dendrites, axons c kh nng pht cc xung in th, chng l cc dy dn tn

hiu t neural i cc ni khc. Ch khi no in th trong soma vt qu mt gi

tr ngng no th axon mi pht mt xung in th, cn nu khng th n

trng thi ngh.

Axon ni vi cc dendrites ca cc neural khc thng qua nhng mi ni

c bit gi l synapse. Khi in th ca synapse tng ln do cc xung pht ra t



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axon th synapse s nh ra mt s cht ho hc (neurotransmitters); cc cht ny

m "ca" trn dendrites cho cc ions truyn qua. Chnh dng ions ny lm

thay i in th trn dendrites, to ra cc xung d liu lan truyn ti cc neural

khc.C th tm tt hot ng ca mt neural nh sau: neural ly tng tt c cc

in th vo m n nhn c, v pht ra mt xung in th nu tng y ln hn

mt ngng no . Cc neural ni vi nhau cc synapses. Synapse c gi

l mch khi n cho php truyn dn d dng tn hiu qua cc neural khc. Ngc

li, mt synapse yu s truyn dn tn hiu rt kh khn.

Cc synapses ng vai tr rt quan trng trong s hc tp. Khi chng ta

hc tp th hot ng ca cc synapses c tng cng, to nn nhiu lin ktmnh gia cc neural. C th ni rng ngi no hc cng gii th cng c nhiu

synapses v cc synapses y cng mnh m, hay ni cch khc, th lin kt gia

cc neural cng nhiu, cng nhy bn.

1.1.1.2. Neural nhn to:

Neural nhn to l mt n v tnh ton c nhiu u vo v mt u ra,

mi u vo n t mt lin kt. c trng ca neural l mt hm kch hot phituyn chuyn i t hp tuyn tnh ca tt c cc tn hiu u vo thnh tn hiu

u ra. Hm kch hot ny m bo tnh cht phi tuyn cho tnh ton ca mng

neural.

Hnh1.2: M hnh mt neural nhn to


wk

y1

y2

b0

yk

fa

u vo u ra a=f( wy+b)


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Mt neural c cu to gm cc thnh phn chnh : lin kt neural, b

cng , hm kch hot.

Lin kt neural l mt thnh phn ca mng neural nhn to lin kt

gia cc neural, n ni u ra ca neural lp ny vi u vo ca mt neuraltrong lp khc. c trng ca thnh phn lin kt l mt trng s m mi tn

hiu i qua u c nhn vi trng s ny. Cc trng s lin kt chnh l cc

tham s t doc bn ca mng neuron, c th thay i c nhm thch nghi

vi mi trng xung quanh.

B cng dng tnh tng cc tn hiu u vo ca neural, c nhn

vi cc trng s lin kt tng ng. php ton c m t y to nn mt b

hp tuyn tnh.

Hm kch hot hay cn gi hm kch hot phi tuyn, chuyn i mt t

hp tuyn tnh ca tt c cc tn hiu u vo thnh tn hiu u ra. Hm kch

hot ny m bo tnh cht phi tuyn cho tnh ton mng neural. N c xem

nh l mt hm gii hn, n gii hn phm vi bin cho php ca tn hiu u

ra trong mt khong gi tr hu hn. M hnh neural trong hnh 1.2 cn bao gm

mt h s iu chnh b tc ng t bn ngoi. H s iu chnh b c tc dng

tng ln hoc gim i u vo thc ca hm kch hot, ty theo n dng hay

m.



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Bng 1.1 : Mt s hm kch hot c bn trong mng neural:

Tn hm Cng thc

hardlim a = 0 vi n < 0

a = 1 vi n 0

hardlims a = -1 vi n < 0

a = 1 vi n 0

purelin a = n

Satlin a = 0 vi n < 0

a = n vi 0 n 1

a = 1 vi n > 1

satlins a = -1 vi n < 0

a = n vi 0 n 1

a = 1 vi n > 1

tansig neeea nn+

=

1

poslin a = 0 vi n < 0

a = n vi n 0

compet a = 1 vi neural c n ln nht

a = 0 vi cc neural cn li

logsigne

a +=1

1

1.1.2. Mng neural nhn to.

L mt h thng bao gm nhiuphn t x l n gin (hay cn gi l

neural) ta nh neural thn kinh ca no ngi, hot ng song song v c

ni vi nhau bi cc lin kt neural. Mi lin kt km theo mt trng s no ,

c trng cho tnh kch hot hoc c ch gia cc neural.



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C th xem cc trng s l phng tin lu tr thng tin di hn trong

mng neural v nhim v ca qu trnh hun luyn ca mng l cp nht cc

trng s khi c thm thng tin v mu hc. Hay ni mt cch khc, cc trng s

u c iu chnh sao cho dng iu vo ra ca mng s m phng hon tonph hp vi mi trng ang xem xt.

M hnh mng neural.

Hnh 1.3: S n gin v mt mng neural nhn to

M hnh mng neural trn gm 3 lp: lp nhp (input), lp n(hidden) v

lp xut (output). Mi nt trong lp nhp nhn gi tr ca mt bin c lp v

chuyn vo mng.

D liu t tt c cc nt trong lp nhp c tch hp ta gi l tng trng

s v chuyn kt qu cho cc nt trong lp n. Gi l n v cc nt trong lp

ny ch lin lc vi cc nt trong lp nhp v lp xut, v ch c ngi thit kmng mi bit lp ny (ngi s dng khng bit lp ny).

Cc nt trong lp xut nhn cc tn hiu tng trng ha t cc nt trong lp

n. Mi nt trong lp xut tng ng vi mt bin ph thuc.



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1.2. c trng ca mng neural.

1.2.1. Tnh phi tuyn.

Mt neural c th tnh ton mt cch tuyn tnh hay phi tuyn. Mt mngneural, cu thnh bi s kt ni cc neural phi tuyn th t n s c tnh phi

tuyn. Hn na, iu c bit l tnh phi tuyn ny c phn tn trn ton

mng. Tnh phi tuyn l mt thuc tnh rt quan trng, nht l khi cc c ch vt

l sinh ra cc tn hiu u vo (v d tn hiu ting ni) vn l phi tuyn.

1.2.2. Tnh cht tng ng u vo u ra.

Mc d khi nim hc hay hun luyn cha c bn n nhng

hiu c mi quan h u vo-u ra ca mng neural, chng ta s cp s

qua v khi nim ny. Mt m hnh hc ph bin c gi l hc vi mt ngi

dy hay hc c gim st lin quan n vic thay i cc trng s lin kt ca

mng neural bng vic p dng mt tp hp cc mu tch lu hay cc v d tch

lu. Mi mt v d bao gm mt tn hiu u vo v mt u ra mong mun

tng ng. Mng neural nhn mt v d ly mt cch ngu nhin t tp hp ni

trn ti u vo ca n, v cc trng s lin kt ca mng c bin i sao cho

c th cc tiu ho s sai khc gia u ra mong mun v u ra thc s camng theo mt tiu chun thng k thch hp. S tch lu ca mng c lp li

vi nhiu v d trong tp hp cho ti khi mng t ti mt trng thi n nh m

khng c mt s thay i ng k no ca cc trng s lin kt. Cc v d

tch lu c p dng trc c th c p dng li trong thi gian ca phin

tch lu nhng theo mt th t khc. Nh vy mng neural hc t cc v d bng

cch xy dng nn mt tng ng u vo-u ra cho vn cn gii quyt.

1.2.3. Tnh cht thch nghi.

Cc mng neural c mt kh nng mc nh l bin i cc trng s lin

kt tu theo s thay i ca mi trng xung quanh. c bit, mt mng neural

c tch lu hot ng trong mt mi trng xc nh c th c tch

lu li mt cch d dng khi c nhng thay i nh ca cc iu kin mi

trng hot ng.



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1.2.4. Tnh cht a ra li gii c bng chng.

Trong ng cnh phn loi mu, mt mng neural c th c thit k

a ra thng tin khng ch v mu c phn loi, m cn v s tin cy ca

quyt nh c thc hin. Thng tin ny c th c s dng loi b ccmu m h hay nhp nhng.

1.2.5. Tnh cht chp nhn sai xt.

Mt mng neural, c ci t di dng phn cng, vn c kh nng chp

nhn li, hay kh nng tnh ton th, vi ngha l tnh nng ca n ch thoi

ho khi c nhng iu kin hot ng bt li. V d, nu mt neural hay cc lin

kt kt ni ca n b hng, vic nhn dng li mt mu c lu tr s suy gimv cht lng.

1.2.6. Kh nng ci t VLSI(Very-large-scale-intergrated).

Bn cht song song s ca mt mng neural lm cho n rt nhanh trong

tnh ton i vi mt s cng vic. c tnh ny cng to ra cho mt mng

neural kh nng ph hp cho vic ci t s dng k thut Very-large-scale-

intergrated (VLSI). K thut ny cho php xy dng nhng mch cng tnh ton

song song quy m ln. Chnh v vy m u im ni bt ca VLSI l mang li

nhng phng tin hu hiu c th x l c nhng hnh vi c phc tp

cao.

1.2.7. Tnh cht ng dng trong phn tch v thit k.

V c bn, cc mng neural c tnh cht chung nh l cc b x l thng

tin. Chng ta nu ra iu ny vi cng ngha cho tt c cc lnh vc c lin

quan ti vic ng dng mng neural. c tnh ny th hin mt s im nhsau:

Cc neural, di dng ny hoc dng khc, biu din mt thnh phn

chung cho tt c cc mng neural.

Tnh thng nht ny em li kh nng chia s cc l thuyt v cc thut

ton hc trong nhiu ng dng khc nhau ca mng neural.

Cc mng t hp (modular) c th c xy dng thng qua mt s tchhp cc m hnh khc nhau.



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1.3. Phn loi mng neural nhn to.

1.3.1. Phn loi theo kiu lin kt neural.

Ta c mng neural truyn thng v neural mng qui hi.Trong mng truyn thng cc neural i theo mt hng nht nh to thnh

th khng c chu trnh, cc nh l cc neural cn cc cnh l cc lin kt

gia chng.

Cc mng qui hi cho php cc lin kt neural to thnh chu trnh, cc

thng tin ra ca cc neural c truyn li cho cc neural gp phn kch hot

chng, nn mng qui hi cn c kh nng lu gi trng thi trong ca n di

dng cc ngng kch hot ngoi cc trng s lin kt neural.

1.3.2. Mt s loi mng neural.

1.3.2.1. Mng dn tin .

C th ni mng neural dn tin l mt kiu mng n gin trong vic sp

t mng. Trong mng ny thng tin ch truyn trn mt hng duy nht. t lp

u vo xuyn qua lp n (nu c) v kt thc ti lp u ra. Khng c chu trnh

hoc vng trong mng.

a. Cc mng dn tin n mc.

Trong mt mng neural phn mc, cc neural c t chc di dng cc

mc. Vi dng n gin nht ca mng phn mc, chng ta c mt mc u vo

gm cc nt ngun chiu trc tip ti mc u ra gm cc neural.

Mc u vo Mc u ra

Hnh 1.4: Mng tin vi mt mc neural



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Nh vy, mng thc s l khng c chu trnh. N c minh ho trong

hnh 1.4 cho trng hp ba nt i vi c mc u ra v u vo. Mt mng nh

vy c gi l mt mng n mc. n mc tc l ch c mt mc, chnh l

mc u ra gm cc nt tnh ton (cc neural). Chng ta khng tnh mc uvo ca cc nt ngun v khng c tnh ton no c thc hin y.

b. Cc mng dn tin a mc.

Lp th hai ca mt mng neural dn tin c phn bit bi s c mt ca

mt hay nhiu mc n, m cc nt tnh ton ca chng c gi l cc neural n

hay cc n v n (thut ng n y mang ngha l khng tip xc vi mi

trng). Chc nng ca cc neural n l can thip vo gia u vo v u ra

ca mng mt cch hu hiu. Bng vic thm mt vi mc n, mng c khnng rt ra c cc thng k bc cao ca tn hiu u vo. Kh nng cc neural

n rt ra c cc thng k bc cao c bit c gi tr khi mc u vo c kch

thc ln.

Mng neural trong hnh 1.5 c gi l kt ni y vi ngha l tt c

cc nt trong mi mc ca mng c ni vi tt c cc nt trong mc tip sau.

Nu mt s kt ni khng tn ti trong mng, chng ta ni rng mng l kt ni

khng y .

Mc u vo Mc n Mc u ra

gm cc nt gm cc gm cc

ngun neural n neural u ra

Hnh 1.5: Mng tin kt ni y vi mt mc n v mt mc u ra



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1.3.2.2. Mng quy hi .

Tri vi mng neural dn tin , mng nn quy hi l nhng m hnh vi

hai lung d liu c hng. Trong khi mng dn tin truyn d liu theo mt

ng thng th nhng mng neural quy hic t nht mt phn hi t nhngneural x l sau quay tr li cc neural x l trc .

Hnh 1.6: Mng hi quy khng c neural n v khng c vng lp t phn hi

Hnh 1.7: Mng hi quy c cc neural n

1.4. Xy dng mng neural.

V c bn ta c th hiu mng neural l mt th c hng nh hnh 1.8.

Trong cc nh ca th l cc neural v cc cnh ca th l cc lin ktgia cc neural.



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Hnh 1.8: S th c hng n gin

V vy xy dng mt mng neural ta xy dng mt th c hng: snh ca th bng s neural trong mng, gi tr ca cc cnh chnh l trng s

lin kt neural.

V d xy dng mt mng neural n gin:

u vo: Cho :

Mng neural c s lp (vi s lp>1).

Mi lp c s neural trong mt lp (s neural>=1).Trng s w lin kit neural ngu nhin trong khong (-a,a).

u ra: Mng neural nhn to.

Kiu d liu: chn lu d kiu mng :

int s lp;

int s neural[s lp];

float w[i][j][k]; vi 2


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w(i,j,k)=random(-a,a)

Bc 5: Nu k


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cc ng dng nm trong vng ca cc bi ton c lng nh m hnh ha

thng k, nn, lc, phn cm.

1.5.1.3. Hc tng cng.

D liu x thng khng c to trc m c to ra trong qu trnh mt

agent tng tc vi mi trng. Ti mi thi im t, agent thc hin hnh ng

yt v mi trng to mt quan st xt vi mt chi ph tc thi Ct, theo mt quy

trnh ng no (thng l khng c bit). Mc tiu l mt sch lc la

chn hnh ng cc tiu ha mt chi ph di hn no , ngha l chi ph tch

ly mong i. Quy trnh hot ng ca mi trng v chi ph di hn cho mi

sch lc thng khng c bit, nhng c th c lng c. Mng neural

nhn to thng c dng trong hc tng cng nh mt phn ca thut tonton cc. Cc bi ton thng c gii quyt bng hc tng cng l cc bi

ton iu khin, tr chi v cc nhim v quyt nh tun t (sequential decision

making) khc.

1.5.2. Thut ton hc.

1.5.2.1. Thut ton hc ca mng neural mt lp.

Xt trng hp perceptron s dng hm kch hot ngng:

>+

=

=

=

d

i

ii

d

i

ii

twv

twv

o u t p u t

1

1

,1

,1

(1.1)

Nu ta cho w0=-t v v0=1, ta c th vit li



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=

>+

=

=

=

=d

i

iid

i

ii

d

i

ii

wv s i gwv

wv

o u t p u t 0

0

0

0,1

0,1

(1.2)

Thut ton:

Thut ton hc ca perceptron hay mng neural mt lp gm 3 bc

chnh:

Bc 1: Khi to:

Khi to trng s w (0 hoc ngu nhin).

Chn tc hc .

Bc 2 : Hc

Vi mi mu (x,t) trong tp hc.

Tnh y=f(x, w).

Nu y!=t thay i vect trng s w vi:

w(mi (c)+ (t-y)x;

Bc 3: lp li bc 2 cho tt c cc mu.

Nhn xt:

Phng trnh w.v=0 l chnh l siu phng trong khng gian d-chiu, suy ra

perceptron c kh nng phn lp tuyn tnh, c kh nng gii bi ton quy hi

tuyn tnh.

Hn ch:

Khng th phn lp phi tuyn.

Gii php: s dng mng neural nhiu tng MLP



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1.5.2.2. Thut ton hc ca mng neural nhiu lp.

Hun luyn mng neural nhiu lp s dng thut ton Lan truyn ngc

gm hai qu trnh: Qu trnh truyn tuyn tnh v qu trnh truyn ngc:

Qu trnh truyn tuyn tnh: D liu t lp nhp qua lp n v n lp xut

:

Thay i gi tr ca trng s lin kt W ca cc neural trong

mng biu din c d liu hc.

Tm ra s khc nhau gia gi tr tht hm mu m mng tnh

c v kt qu d on ca mng gi l li (hc c gim st).

Qu trnh truyn ngc: Gi tr li s c truyn ngc li sao cho qutrnh huyn luyn(hc) s tm ra trng s Wi li nh nht.

Thut ton:

Xt mng neural 3 lp : input, hiden v output.

Hm kch hot cc neural : logistic (sigmoid).

g(x)= (1.3)

Bc 1: Khi to trng s w ngu nhin nh.

Bc 2 : Chn lp u vo x v nh n vo lp u vo .

Bc 3 : Truyn s kch hot qua trng s n khi kich hot cc neural u

ra.

Bc 4: Tnh o hm ring E theo trng s cho lp xut. s dngGRADIENT ca hm li .

Bc 5: Tnh o hm ring E theo trng s cho lp n. s dngGRADIENT ca hm li.

Bc 6: Cp nht tt c trng s theo Wi=W(i-1)-(E/ Wi)

Bc 7: quay lai Bc 2 cho n Bc 6 cho tt c cc mu.

Trong : GRADIENT hm li:



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i vi cc neural lp u ra:

Hm li:

2)1(2

1)( = zzE

(1.4)

( t l gi tr tht ca mu hun luyn)

o hm ring ca hm li theo trng s b:

b

v

v

z

z

E

b

E

=

(1.5)

Ta c:

>

==

=

=

=

0,

0,1

)1(

)(

1 iy

i

b

v

zzv

g

v

z

tzz

E

i

t:

)1()( =

= zztz

v

z

z

Ep

Ta c:

>

==

0

0

ipy

ip

b

E

ii

(1.6)


w2

wk

w1 z=g(v)

v=b0

+

g(x)=

y1

y2

b0y

k


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i vi cc neural lp n:

o hm ring ca hm li theo trng s:

a

u

u

y

y

E

a

E

=

(1.7)

Ta c:

( )

>

==

=

=

==

=

=

0,

0,1

1

)1()(

1

jc

j

a

u

yyu

y

by

v

pzztzv

z

z

E

y

v

v

z

z

E

y

E

jj

ii

iiiii

i

i

i

K

i

i

i

i

i

t:

)1(1

yybpu

y

y

Eq

K

i

ii

=

= =

Ta c:

>

==

0

0

1 iqx

iq

a

E

i

(1.8)


a2

ad

a1

y=g(u)

v=a0

+

x1

x2

a0

Lp ura


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Sau khi tnh c o hm ring ca hm li theo tng trng s, trng s

s c iu chnh bng cch tr bt i 1 lng bng tch ca o hm ring v

tc hc:

i

iiwEww= (1.9)

Nhng hn ch ca phng php lan truyn ngc:

Ngoi nhng thnh cng ca gii thut hc lan truyn ngc, vn cn c

mt s kha cnh lm cho gii thut tr nn cha c bo m l mi lc u

tt. Kh khn ch yu l qu trnh hun luyn lu. C th do nhp hc v

ng lc khng ti u. S sai st trong vic hun luyn ni chung xut hin t

hai ngun: mng lit v nhng cc tiu a phng.

Mng lit: xy ra khi nhng trng s c iu chnh ti nhng gi tr rt

ln. Tng u vo ca mt n v n hoc n v u ra c th bi vy m t

gi tr rt cao (hoc dng hoc m), v qua hm kch hot sigmoid, n v s

c mt gi tr kch hot rt gn 0 hoc rt gn 1. Gi tr hiu chnh trng s gn

0, v qu trnh hun luyn c th i n mt trng thi dng o.

Cc tiu a phng: b mt sai s ca mng rt phc tp y nhng ngni v nhng thung lng. Bi v s h dc, mng c th b mc by ti mt

cc tiu a phng khi c nhiu cc tiu thp hn gn bn cnh. Nhng

phng php thng k c th gip trnh ci by ny, nhng chng lm chm.

Mt phng n khc l tng thm s lng n v n. Nh vy s lm vic trong

khng gian sai s nhiu chiu, nn c hi gp by nh hn. Tuy nhin vic tng

cng c gii hn trn, khi vt qua gii hn ny, c hi mc by li tng ln.

1.6. Thu thp d liu cho mng neural.

Mt khi ta quyt nh gii quyt mt vn s dng nhng mng neural ta

cn phi thu thp d liu cho mc tiu hun luyn. Tp hp d liu hun luyn

bao gm mt s trng hp, mi trng hp cha nhng gi tr ca u vo v

u ra khc nhau. Nhng vic u tin cn lm l: nhng bin no c s

dng, bao nhiu trng hp cn thu thp.

S la chn do trc gic quyt nh. Cng vic chuyn mn ca ta tronglnh vc cn gii quyt s cho ta nhng tng v cc bin u vo ph hp.



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Trong nhng mng neural ta c th chn v loi b nhiu bin v mng neural

cng c th xc nh bng qu trnh thc nghim. Trong mt bc ta nn tnh

n bt k bin no m ta ngh c nh hng n qu trnh thit k.

Nhng mng neural x l d liu s trong mt tm gii hn r rng. iuny a ra mt vn , nu d liu nm trng mt vng c bit nh d liu

cha bit hay khng phi d liu s. Th phi c nhng phng php x l thch

hp, chng hn. D liu s c chia nh thnh nhng khong thch hp cho

mng v nhng gi tr thiu c th thay th bng gi tr trung bnh hay gi tr

thng k ca bin thng qua nhng bin khc c hun luyn.

X l d liu khng phi s th kh hn. Loi d liu khng phi l s

thng thng nht l nhng bin c gi tr nh danh nh gii tnh(nam, n).Bin nh danh c th biu din bng s hc v mng neural c chc nng hi

tr iu ny. Tuy nhin, mng neural lm vic tt vi nhng trng hp bin

nh danh l mt tp nhiu gi tr.

S trng hp mu dng hun luyn mng rt kh xc nh. c mt

vi hng dn v mi lin h gia s trng hp mu vi kch thc mng(cch

n gin nht l s trng hp mu gp 10 ln s kt ni trong mng). Thc ra

s trng hp mu cng c lin quan n phc tp ca hm m mng phi

hc. Khi s bin tng ln, s trng hp mu cn hun luyn cng tng phi

tuyn, v th vi s cc bin nh(50 hoc nh hn) th li cn mt s ln cc

trng hp mu.

Trong hu ht cc vn trong thc t, s trng hp mu l khong hng

trm hay hng nghn mu. i vi nhng vn rt phc tp th cn nhiu hn,

nhng trng hp ny rt t. Nu d liu hun luyn t hn, r rng khng

thng tin hun luyn mng, v cch tt nht l dng mng tuyn tnh. Nhiu

vn trong thc t c d liu khng ng tin cy, mt vi d liu b ph hng

do liu do nhiu, hoc cc gi tr khng phi hp c vi nhau. Mng neural

c kh nng c bit x l d liu b mt(s dng gi tr trung bnh hay cc

nhng gi tr thng k khc). Mng neural cng chu c nhiu, nhng cng

phi c gii hn. Nu thnh thong c gi tr nm xa ra khi vng gi tr bnh

thng th mng hun luyn phi c ngng. Cch tt nht i vi trng hp

ny l nhn ra v loi b nhng gi tr nm xa ( c th hy trng hp ny



23/59


24/59


ca mng neural l hc mt m hnh ca th gii thc t c mt s mc

ch xc nh cn quan tm. Tri thc ca th gii bao gm hai loi thng tin sau:

Trng thi th gii bit, c biu din bi cc s kin v nhng

ci bit; dng tri thc ny c xem nh l cc thng tin ban u.

Cc quan st(o c) v th gii, thu nhp c thng qua cc b

cm bin c thit k thm d mi trng m trong mng

hot ng. Ni chung, cc quan st ny lun b nhiu v sai lch do

nhiu nguyn nhn khc nhau. Cc quan st thu nhn c nh vy

cung cp mt qu thng tin, m t ly ra cc v d c dng

hun luyn mng neural.

Do cu trc mt mng neural l v cng a dng, nn c th biu din

tri thc mt cch c hiu qu, ngi ta a ra bn quy tc chung sau:

Quy tc 1. Cc u vo tng t t cc lp tng t cn phi lun to ra

nhng biu din tng t trong mng, v nh vy nn c phn lp thuc v

cng mt loi. Trong tiu chun ny, ngi ta thng s dng mt s thc o

xc nh tng t gia cc u vo (v d khong cch euclide).

Quy tc 2. Cc phn t m c th phn ra thnh cc lp ring bit th nnc nhng biu din khc nhau ng k trong mng.

Quy tc 3. Nu mt c trng no c bit quan trng th nn c mt s

lng ln neural lin quan n vic biu din c trng ny trong mng. S

lng ln cc neural bo m mc chnh xc cao trong vic thc hin cc

quyt nh v nng cao kh nng chu ng cc neuron hng.

Quy tc 4. Thng tin ban u v cc tnh cht bt bin nn c a vo

trong thit k ban u ca mt mng neural, v nh vy s gim bt gnh nng

cho qu trnh hc. Quy tc 4 c bit quan trng v nu chng ta p dng n mt

cch thch hp s dn n kh nng to ra cc mng neural vi mt kin trc

chuyn bit. iu ny thc s c quan tm do mt s nguyn nhn sau:

1. Cc mng neural th gic v thnh gic sinh hc c bit l rt chuyn

bit.

2. Mt mng neural vi cu trc chuyn bit thng c mt s lng nhcc tham s t do ph hp cho vic chnh l hn l mt mng kt ni y .



25/59


Nh vy mng neural chuyn bit cn mt tp hp d liu nh hn cho vic tch

lu; n hc s nhanh hn, v thng c kh nng tng qut ho tt hn.

3. Tc chuyn thng tin qua mt mng chuyn bit l nhanh hn.

4. Gi ca vic xy dng mt mng chuyn bit s nh hn do kch thcnh ca n so vi mng kt ni y .

1.8. Mt s vn ca mng neural.

Khi xy dng mt ng dng mng neural chng ta cn quan tm mt s

vn sau:

Vn v kin trc mng neural : neural no ni vi neural no? y

chnh l s la chn m hnh ca mng neural. N s ph thuc vo s trnh

by d liu v ng dng. Nhng m hnh phc tp qu dn n nhng vn

la chn qu trnh hun luyn hay l vic la chn gii thut hc.

La chn gii thut hc: y c nhiu s cn bng gia cc gii thut

hc. Gn nh bt k gii thut no s lm tt vi chnh xc ca cc siu tham

s cho vic hun luyn trn tp d liu c nh cho trc. Tuy nhin s la chn

v iu hng ca gii thut cho vic hun luyn trn cc tp d liu ny cn

thc hin nhiu th nghim, l iu rt quan trng. Trn mt m hnh nu la

chn gii thut v hm nh gi ph hp th mng neural c th cho kt qu rt

tt.

Trng s ca cc cung ni v ngng thay i thng xuyn. c nhiu

nghin cu v vn ny v cng c mt s kt qu :

Nu mng gy ra li, th c th xc nh neural no gy ra li => iu chnh

neural .Vi cch tip cn ny, mng phi bit rng n gy ra li.

Trong thc t, li ch c bit sau mt thi gian di.

Chc nng ca nt neural khng qu n gin nh m hnh. Bi v mng

neural hot ng nh mt hp en.

Mt s hng dn khi s dng mng neural.



26/59


Xy dng mng khi to(dng mt lp n c s neural= tng s neural

ca lp nhp v l p xut).

Hun luyn mng dng cc gii thut hun luyn. Nn thc hin trn nhiu

mng khc nhau trnh trng hp cc tiu cc b.Nu my Khng thuc bi => thm mt vi neural cho tng n.

Ngc li nu my Hc vt=> bt mt vi neural ra khi tng n.

Khi tm c mt kin trc mng tng i tt ly mu li tp d liu

v hun luyn li tm cc mng mi.

1.9. ng dng ca mng neural.

Mng neural trong mt vi nm tr li y c nhiu ngi quan tm

v p dng thnh cng trong nhiu lnh vc khc nhau, nh ti chnh, y t,

a cht v vt l. Tht vy, bt c u c vn v d bo, phn loi v iu

khin, mng neural u c th ng dng c. V d nh kh nng nhn dng

mt ngi trong cc h thng qun l thng tin lin quan n con ngi (qun l

nhn s cc cng s, doanh nghip; qun l hc sinh, sinh vin trong cc

trng trung hc, i hc v cao ng; ); cc ngnh khoa hc hnh s, ti

phm; khoa hc tng s, t vi,

Kt hp cht ch vi logic m, mng neural nhn to to nn cuc cch

mng thc s trong vic thng minh ha v vn nng ha cc b iu khin k

thut cao cho c hin nay v trong tng lai. V d nh ng dng t ng iu

khin h thng li tu, h thng d bo s c,

Mng neural da trn vic m phng cp thp h thng neural sinh hc.

Trong tng lai vi s pht trin m phng neural sinh hc, chng ta c th cloi my tnh thng minh tht s.



27/59


CHNG 2:NG DNG MNG NEURAL NHN DNG K T

2.1. Gii thiuNhn dng k t l mt ng dng ang c rt nhiu ngi quan tm

nhng n y kh khn v th thch.

iu rt kh ca kh nng nhn dng ph hp k t l cc kiu ngn ng

rt phc tp khng theo quy lut do bin i trong font, kiu v kch c.

Vi mt s phng thc lp trnh truyn thng nh x nh k t vo

trong ma trn, phn tch nh hoc vector d liu, kim tra a ra quyt nh ph

hp ca kt qu. Vic thc thi ny trong lp trnh truyn thng cn vit m

ngun v tn cho mi kiu i vi s khng nht qun hay s trnh lch vi cc

gi tr u ra khc nhau. L thuyt ny khng hin thc.

S dng mng neural nhn to vi nhng mng lm vic ng quy tc t

vic cp nht li cc trng s lin kt gia cc nt mng. Vi u im l mng

c th nhn d liu t nhng phn tch sinh ng ca cc nh u vo v vic

hun luyn cho cc k t u ra cho mu ni cch khc l kh nng thch nghivi mi trng d liu u vo sinh ng.

2.2. Pht biu bi ton

Cho bi ton nhn dng k t vi u vo l trang vn bn trn nh dng

file nh (*.bmp,*.jmp,). Yu cu l xy dng chng trnh nhn dng k t

vn bn trn file nh. S dng cng c l mng nron v u ra l tp hp cc k

t l tr di dng vn bn.

Gi thit giai on tin x l c thc hin : nh c phn

ngng, xoay nh, lc nhiu... ti ny ch i su nghin cu qu trnh nhn

dng k t ca mng neural.

tng bi ton :

Phn tch nh cho k t: Chia nh theo dng v tch k t theo tng vng

gii hn

Chuyn i k t sang ma trn im nh.



28/59


Chuyn thnh ma trn tuyn tnh v a vo mng neural.

a v mng neural tnh gi tr u ra.

Hin th k t ca m Unicode thu c.

Cc bc gii quyt bi ton s dng mng neural nhn dng k t: Xy

dng mng, x l d liu(phn tch nh), hun luyn mng nueral v nhn dng

mng neural

2.3. Cc bc gii quyt gii quyt bi ton

2.3.1. Xy dng mng neural.

Chn mng a tng Feedforward vi 3 lp :

Hnh 2.1: S mng neural thit k


500neuralLpn

150neuralLpuvo

im nh

im nh

im nh

im nh

0 hoc 1

0 hoc 1

0 hoc 1

0 hoc 1

16neuralLpu

ra


29/59


Lp u vo gm 150 neural nhn gi tr nh phn(0,1) ca 150 thnh

phn ca vct tng ng. d liu c vc t ha t ma trn im nh k t

bng phng php chia li.

Lp n gm 500 neural, s neural ny c quyt nh t nhng kt quti u v gi tr li c s trong qu trnh hun luyn.

Lp u ra gm 16 neural a ra gi tr nh phn(0,1) tng ng vi 16

bt ca m Unicode.

Vi nhng lp ni trn ta xy dng c mng neural nh hnh 2.1.

2.3.2. X l d liu (phn tch nh).

Qu trnh phn tch nh tm ra c tnh ca k t bi vic kim tra imnh n l gi tr u vo cho c qu trnh hun luyn v qu trnh kim tra. Qu

trnh phn tch ny da trn vic nhn dng t nh u vo bng phng php

tnh gi tr mu. Gii hn ca gi tr l im en RGB(0,0,0) hoc im trng

RGB(255,255,255). Nhng nh u vo c nh dng bitmap(*.bmp).

2.3.2.1. Tch dng k t.

S lit k cc dng ca k t trong mt nh k t hay mt trang vn bn lmt trong yu t quan trng trong qu trnh tm gii hn ca k t, khi tm gii

hn ca k t tip theo chng ta khng cn qut trn ton b nh.

Thut ton:

1. Bt u t im nh x, y u tin (0,0), v t l dng 0.

2. Qut n ht chiu rng ca nh trn mt gi tr y ca nh.

3. Nu l pht hin im en th lu gi tr y l nh ca hng u tin:

Nu khng xt tip im tip theo.

Nu khng thy im en no th tng y v khi ng li x qut

dng ngang tip theo.

Bt u t nh cu hng tm thy (0,gii hn trn).

4. Qut n ht chiu rng ca nh trn mt gi tr y ca nh.



30/59


Nu khng pht hin im en no th nh du gi tr y-1 l gii

hn di ca hng. V tng s dng, xt dng tip theo.

Nu vn pht hin thy im en tng y v khi ng li x xt hng

ngang tip theo.

5. Bt u t gii hn di ca hng ngang tm thy sau cng lp li t bc 1

n bc 4 tm dng k tip.

6. Nu y bng chiu cao ca nh th dng.

Hnh 2.2: Qu trnh tch dng k t

2.3.2.2. Tch k t.

Thut ton

1. Bt u t k t u tin ca hng trn cng vi gi tr x u tin.

2. Qut ht chiu rng vi mt gi tr y.

Nu pht hin im en nh du y nh l nh ca hng u

tin.

Nu khng xt im tip theo.

3. Bt u t gii hn trn ca k t pht hin c v gi tr x u

tin.(0,gii hn trn k t) .


nh u vo

Qutrnhtchdng

Gii hn trnGi hn di


31/59


4. Qut n gii hn di ca dng, gi nguyn x.

Nu pht hin im en nh du x l pha tri ca k t.


Nu khng thy im en no tng x v khi ng li y

xt ng thng ng tip theo.

5. Bt u t pha tri ca k t tm thy v nh ca dng hin thi,

(gii hn tri k t, gii hn trn dng).

6. Qut ht chiu rng ca nh. Trn cng mt gi tr x.

Nu khng c im en no th nh du x-1 l bn phi ca

k t.

Nu pht hin im en tng x v khi ng li y xt

ng thng ng tip theo.

Hnh 2.3: Qu trnh tch k t

2.3.2.3. Tm gii hn k t.

Trong mt s trng hp qu trnh tch k t c th khng phi l gii hn

thc t ca k t. y xut hin vn khng sp xp k t theo quy lut nh

sp xp dng k t. Tc l nh ca mt hng khng tt yu l nh ca tt c v

tng t y ca ca mt hng cng khng l y ca tt c cc k t trn mt

dng. T y cn c mt th tc tm gii hn k t.


x

y

Qu trnhtch k t

(0,0)

Gihnphik t

Gihntrik t


32/59


Thut ton

1. Bt u t nh ca dng hin thi v bn tri ca k t.

2. Qut n bn phi ca k t. cng mt gi tr y.

Nu pht hin im en th nh du y v thay i li gii

hn trn.


Nu khng tm thy im en no tng y v khi ng li x,

xt ng thng ngang tip theo.

3. Bt u t gii hn di ca dng v bn tri ca k t.

4. Qut ti bn phi ca k t trn mt gi tr y.

Nu pht hin im en, nh du y l gii hn di ca k

t.

Nu khng pht hin im en gim y v khi ng li x xt

ng thng ngang tip theo.

Hnh 2.4: Qu trnh tm gii hn k t


Qutrnhtmgiihn

Gi hn trnk t

Gi hn dik t


33/59


2.3.2.4. nh x vo ma trn

Bc tip theo l ta phi nh x nh ca k t vo mt ma trn nh phn hai

chiu tng ng. Mt vic rt quan trng y l vic quyt nh c ca ma

trn. Nu cc im nh ca k t c nh x vo ma trn. tuy nhin vic nydn n vic x l cc ma trn rt ln. cho cn bng hp l ta s chun ha

c ca ma trn bng 10x15 vi 150 phn t.

Thut ton:

1. i vi chiu rng:

Khi to vi 10 phn t tng ng.

nh x im u (0,y) v im cui (C_rong,y) ca nh k ttng ng vi gi tr u (0,y) v gi tr cui (10,y) ca ma trn.

Chia nh chiu rng thnh 10 gi tr tng ng.

2. i vi chiu cao:

Khi to vi 15 phn t tng ng.

nh x im u (x,0) v im cui (x,C_cao) ca nh k t

tng ng vi gi tr u (x,0) v gi tr cui (x,15) ca ma trn.

Chia nh chiu cao thnh 15 gi tr tng ng.

Hnh 2.5: Qu trnh chia li k t


0

15

0 10

(0,0)

(10,15)


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a gi tr vo mng neural ta cn chuyn ma trn im nh sang ma

trn gi tr.

Thut ton:

1. Bt u t phn t (0,0).

2. Tng x gi nguyn gi tr y cho ti khi bng chiu rng ca ma trn.

nh x mi phn t ti mt phn t ca mng tuyn tnh.

Nu l im en th nhn gi tr bng 1.

Ngc lI nhn gi tr bng 0.

Nu x = chiu rng th khi ng li x v tng y.Lp li cho ti khi (x,y)=( C_Rong, C_Cao).

Hnh 2.6: Qu trnh nh x t ma trn im sang ma trn gi tr.

2.3.3. Hun luyn mng neural.

Mt mng neural c xy dng s phi c hun luyn trn mt

khng gian u vo c chun b trc. Khi hot ng mng neural s c

gi tr c hun luyn.

Mt vi vn cn thit cho vic hun luyn mng:

Ti sao li c s khc nhau ca khng gian u vo? Mi mt u vo khc

nhau gi tr ngu nhin v trong mt phm vi gii hn khng c gi tr lung no

d on c gia cc gi tr ca n.



35/59


Ti sao c s phc tp ca cc tham s cho vic hun luyn mng? Cc

tham s phc tp l cc k t thng thng bi cc c trng chng lp v kch

c d liu cao.

Ci g cn c s dng cho nhng gi tr ca :Tc hc.

H s gc Sigmoid.

Trng s kt ni c s.

C bao nhiu ln lp cn thit cho vic hun luyn mng ca mt tp u

vo?

Gi tr ngng ca li l bao nhiu c s dng so snh tng phntrong vic xc nh qu trnh dng ca vic lp li nu c nhu cu xut hin.

S phc ca cc d liu tham s ring l cng l vn khc trong qu

trnh nhn dng. Mi mt k t li c mt s ln c tnh phn bit m cn phi

tnh ton nhn dng n mt cch chnh xc. S loi b mt s c tnh c th

c kt qu ca trong s tng ng ca cc mu. S ti thiu ca d liu yu

cu cho n l mt trong nhng phn phc tp nht ca khng gian u vo trong

vic nhn dng.

Thut ton:

1. Xy dng mng tng ng vi m hnh tham s.

2. Khi to gi tr trng s vi gi tr ngu nhin. Np file hun luyn

(c nh u vo v u ra mong mun).

3. Phn tch nh v nh x tt c k t tm thy vo cc mng mt chiu.

4. c gi tr u ra mong mun t file v chuyn i tng k t ti gi

tr nh phn Unicode v lu tr ring bit.

5. Vi mi k t:

Tnh ton gi tr u ra ca mng Feed ForWard.

So snh vi gi tr u ra mong mun tng ng vi tng k t

v tnh ton li.



36/59


truyn ngc gi tr t u v vi mi lin kt iu chnh

trng s lin kt.

6. Chuyn sang k t tip theo v lp li 6 cho ti khi ht cc k t.

7. Tnh ton trung bnh li cho tt c cc k t.

8. Lp li t bc 6 n 8 cho ti khi t s a vo ca s ln lp ti

a.

vi phm vi li t n ngng. Nu nh vy th b lp li.

ngc li tip tc lp li.

S khi qu trnh hun luyn c ch ra trong hnh 2.7.



37/59


Hnh 2.7: S khi qu trnh hun luyn mng neural

2.3.4. Nhn dng nh k t.

Qu trnh nhn dng ca mng neural n gin v d hiu. Khi chng

trnh chy s gi cc modun: phn tch nh, vector ha... trong qu trnh hun

luyn c th c s dng li trong qu trnh nhn dng. Nhng bc c s

nhn dng nh ca k t c th tm tt bi s hnh 2.8 di y:


S

S

BT U

Tnh ton u ra

Dng u tin

nh x k t ti vector

Phn tch dng nh

Chuyn t Unicode sang k t

Ht k t trndng ?

Ht Cc

dng ? Dng tip theo

K t tip theo

KTTHC

S

S

S

S

Cp nht trng s

BT U

Xy dng mng

Khi to trng s

Np file hun luyn

Phn tch nh

Pht hin k t tiptheo

Cc kt snsng ?

Cc k

t snsng ?

c u ra mongmun

Tnh u ra ca

mng

Tnh li

Cc kt snsng ?

Li

ung dung mang neural trong nhan dang ki tu 4538

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