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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
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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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
Bi Quang Chin Trang 5
wk
y1
y2
b0
yk
fa
u vo u ra a=f( wy+b)
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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
w(i,j,k)=random(-a,a)
Bc 5: Nu k
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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
=
>+
=
=
=
=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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n tt nghip ng dng mng neural trong nhn dng k t
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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n tt nghip ng dng mng neural trong nhn dng k t
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)
Bi Quang Chin Trang 19
w2
wk
w1 z=g(v)
v=b0
+
g(x)=
y1
y2
b0y
k
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n tt nghip ng dng mng neural trong nhn dng k t
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)
Bi Quang Chin Trang 20
a2
ad
a1
y=g(u)
v=a0
+
x1
x2
a0
Lp ura
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n tt nghip ng dng mng neural trong nhn dng k t
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.
Bi Quang Chin Trang 21
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n tt nghip ng dng mng neural trong nhn dng k t
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
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n tt nghip ng dng mng neural trong nhn dng k t
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 .
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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
Bi Quang Chin Trang 28
500neuralLpn
150neuralLpuvo
im nh
im nh
im nh
im nh
0 hoc 1
0 hoc 1
0 hoc 1
0 hoc 1
16neuralLpu
ra
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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) .
Bi Quang Chin Trang 30
nh u vo
Qutrnhtchdng
Gii hn trnGi hn di
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n tt nghip ng dng mng neural trong nhn dng k t
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 xt im tip theo.
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.
Bi Quang Chin Trang 31
x
y
Qu trnhtch k t
(0,0)
Gihnphik t
Gihntrik t
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n tt nghip ng dng mng neural trong nhn dng k t
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 xt im tip theo.
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
Bi Quang Chin Trang 32
Qutrnhtmgiihn
Gi hn trnk t
Gi hn dik t
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n tt nghip ng dng mng neural trong nhn dng k t
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
Bi Quang Chin Trang 33
0
15
0 10
(0,0)
(10,15)
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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.
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n tt nghip ng dng mng neural trong nhn dng k t
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:
Bi Quang Chin Trang 37
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
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