2
2.1 . 1
2.2 . 10
2.3 . 16
2.4 . 21
2.5 . 24
2.5.1 . 25
2.5.2 . 32
2.5.3 . 36
2.6 . 37
2.7 . 52
. . . ARIMA, 1970- ., . - . AR () (q), ARMA (, q), . . (. [ Chatf.2,3.1.4; Wei,p.38, Brockwell,p.54. ]
......) .
() ,
(2.1)
(2.1) 1,..., ; at σ2, .. at ~ WN (0,σ2).
(2.1) AR (p) (autoregressive process). ,
F x 1, 2,..., r e : , F x 1, 2,..., r. (2.1) t , . , , t ( ) at, .
, ov (Xt s, at) = 0 s > 0; , at , at t. , t at.
|
|
(1.10), . ,
(2.1)
䠠
(2.2)
- .
- AR (p) .
zp 1 zp -1 - 2 zp -2 - - = 0. (2.3)
, (2.3) ( ), AR (p) .
AR (p). (2.1) t - k,
, (, Eat = E t = 0, E ( t - h at) = 0 h > 0 E ( t at) = s 2 a)
(2.4)
(2.4) D t, ,
(2.5)
堠
AR (1) AR (2).
(2.1) AR (1)
(2.6)
.2.1 AR (1) c = 0,8; X 0 =0, (2.6) at ~ N (0, 1).
.2.1. AR (1) = 0,8
(2.6) 堠 z - = 0 z = < 1 .
AR (1)
Var (Xt) = σ a 2 / (1 - 12),
, 12 < 1. , . , AR (1) : - 1 < 1 < 1.
γ h = 1 γ h 1 h > 0.
C
ρ h = 1 h h > 0. (2.7)
, , , 1. 0 < 1 < 1, - ; -1 < 1 < 1, . (2.7) .2.2.
) )
.2.2. AR (1)
|
|
( - 1 = 0,8; - 1 = - 0,8)
.2.2, ( ) ( ).
AR (1) (1.5)
, , h.
, AR(1) 1. , () k > 1.
, ( - , : causal) , . , - . , , AR (1), (2.6) . , , (2.6) , Xt at, , , . AR (1) (, ), . , . , = 1, . [ Chatf.2,3.1.4; Wei,p.38, Brockwell,p.54.]
(2.1) AR (2)
Xt = 1 Xt - 1 + 2 Xt - 2 + at. (2.8)
.2.3 AR (2) 1=1,2; 2= - 0,35, (2.8) at ~ N (0, 1).
.2.3. AR (2)
, ,
W (z) = z 2 / (z2 1z 2),
z 2 1 z 2= 0. (2.9)
AR (2) , (2.9) . AR (2),
(2.10)
ω1 ω2. - ,
z 2 1 z 2= (1 - ω1 ) (1 ω2 ).
(2.10) , .. 12 + 4 2 < 0, ω1 ω2 . , AR (2) , , [Wein,3.1.16. p.40]:
(2.11)
(2.11)
(2.12)
(2.5) AR ( 2)
ρ k = 1ρ k -1 + 2ρ k -2 k > 0. (2.13)
, , 1,
ρ1 = 1 ρ0 + 2ρ-1 = 1+ 2ρ1.
AR (2) :
ρ0 = 1; ρ1 = 1/ (1 - 2); ρ k = 1ρ k -1 + 2ρ k -2 k ≥ 2.
.2.4 AR(2 ) : .2.4. - 1 = 1,2; 2 = - 0,35; .2.4. - 1 = 0,6; 2 = - 0,4. [0,36 +4 (-0,4) = -1,24 < 0], . 2.4..
|
|
)
)
.2.4. AR (2)
AR (2) (1.5) (2.13) :
(2.14)
(2.14) , . , , kk = 0 k ≥ 3, , AR (2) , .
() (Moving Average - MA) . , . q - MA (q) -
(2.15)
q 1,..., q q .
(2.15) (q), at.
, (2.15)
(2.16)
(2.16) θ() q.
(2.16) , t q (B), at. (2.15), t n ≥ q at, t 1 ,..., t q , . n ≥ q E { t } = 0.
, , - [1974.], (2.15) , -, , θ() , (2.2) () AR (p). , θ - , [Chatf.,2, point. 3.1.2].. ?
MA (q) . . , { at } { at * } - . , (1), ꠠ Xt = at + θ t 1 蠠 Xt = at * + θ-1 * t 1, . , θ() , . , (1) . , θ() . , (2.15)
(2.17)
|
|
π j ,
, () , at, Xt at Xt . π j (2.17) , . , MA (q): θ() AR (p): () . , AR (p) , MA (q) [Wei,p.57].
(2.15) ,
(, γ k k ³ 0).
(2.18)
, (q) q, . , r 1,..., r q , q (2.18) q 1,..., q q. q (.. q).
, , .
AR () (q): AR () τ → ∞ ( ) , (q) τ = q .
(1.1). , , (purely indeterministic), .. , (2.15). ,
(2.19)
ψ0 = 1; { at } σ2.
(2.19) (∞), . , , . , , { at } , , (2.19) - ∞ + ∞. , { at } , . . (∞) , . , , .
. . (1) (2.15)
Xt = at + θ1 t 1. (2.20)
Var(Xt) = σ a 2 + θ12 σ a 2 = (1 + θ12) σ a 2,
at t 1 .
(1) (2.20) Xt k,
Xt k Xt = Xt k at + θ1 Xt k t 1 ,
,
γ1 = θ12 σa2, γ k = 0 k > 1.
(2.21)
, (1) , 1, , . , , (1) , 1, .. (1) "", , !
|
|
(1.5) (2.21)
, , . AR (1) (1). (1) , , AR (1) . , , (1) AR (1) , .
(2)
Xt = at + θ1 t 1 + θ2 t 2. (2.22)
ꠠ
ρ1 = (θ1 + θ1 θ2) / (1 + θ12 + θ22),
ρ2 = (θ2) / (1 + θ12 + θ22), (2.23)
ρ k = 0 k > 2.
, 2. - , , (q) , q, , ρ k = 0 k > q. , (q) , , q, , " ".
(2) , ( , (2.22), ), ( ).
.2.6 (1) θ1 = 0,5 (2) θ1 = 0,5; θ2 = 1,0.
)
)
.2.6. (1) ( - θ1 = 0,5) (2) ( - θ1 = 0,5; θ2 = 1,0)
R () (q) q . - . , . - , .. RMA (, q), 䠠
Xt = 1 Xt -1 + + p Xt -p + at + θ1 t 1 ++ θ q t q (2.24)
() Xt = θ() at, (2.25)
(B), q (B) - , R () (q).
, RMA (, q) , ( ) RMA (, q), R () (q).
(2.25) :
{ Xt } AR - , .. AR (), θ()= 1 () Xt = et, et q, .. et = θ() at;
{ Xt } - q, .. MA (q), ()= 1 Xt = θ() bt, bt , .. () bt = at.
, () Xt = θ() at.
, (2.24) . (2.25) , () = 0 . , , θ() = 0 .
(2.24) , , - .
(2.24)
Xt - k
.
,
, RMA (, q)
(2.26)
RMA (, q), (2.26), q, AR -, . q , . .
: RMA (q), RMA (, q) , (B) = 0 q (B) = 0.
RMA (1,1) (2.24) 젠
Xt = 1 Xt - 1 + at + θ1 t 1. (2.27)
RMA (1,1) R (1) , MA (1). . (2.27),
E (Xt) - 1 E (Xt -1) = E (at) + θ1 E ( t 1).
E (ai) = 0 i, Xt
E (Xt) = 0.
.
t ,
E (Xt t) = 1 E (Xt -1 t ) + E (at2) + θ1 E ( t t 1) = E (at2) = σa2. (2.28)
RMA (1,1). (2.28) (Xt - h),
Xt Xt - h = 1 Xt Xt - h + at Xt - h + θ1 Xt - h t 1.
h = 1, (2.28),
γ1 - 1γ0 = θ1 σa2.
R (1), γ h - 1γ h 1 = 0. h = 2 , γ 2 - 1γ1 = 0. R (1). ,
γ h - 1γ h 1 = 0 h > 1. (2.29)
RMA (1,1)
ρ1 = 1+ θ1 σa2 / γ 0, ρ h = 1ρ h 1 h > 1, (2.30)
γ 0 - RMA (1,1).
, RMA (1,1) R(1) , h = 2, , RMA (1,1) . .2.7 , (2.30), 1=0,8; θ1=0,5; σa2 = 1; γ 0 = 2.
.2.7 ARMA (1,1)
ARMA (1,1) 1 = θ1 = 1 .2.8.
(2.24) , AR - MA - RMA (, q), B
(1 - 1 -... p p) = (1 + θ1 +... + θ q q). (2.31)
.2.8. ARMA (1,1)
(2.31) AR -; - MA - . AR MA . (, q) . "" AR - AR - RMA (, q). , 1, RMA (, q) - .