' TV_GARCH.PRG (10/10/2000)
' example program for EViews LogL object
' revised for version 5.0 (11/19/2009)
'
' restricted version of 
' tri-variate BEKK of Engle and Kroner (1995):
'
'  y = mu + res 
'  res ~ N(0,H)
'
'  H = omega*omega' + beta H(-1) beta' + alpha res(-1) res(-1)' alpha'
'
'  where,
'     y = 4 x 1
'    mu = 4 x 1
'     H = 4 x 4 (symmetric)
'         H(1,1) = variance of y1   (saved as var_y1)
'         H(1,2) = cov of y1 and y2 (saved as cov_y1y2)
'         H(1,3) = cov of y1 and y2 (saved as cov_y1y3)
'         H(1,4) = cov of y1 and y4 (saved as cov_y1y4)
'         H(2,2) = variance of y2   (saved as var_y2)
'         H(2,3) = cov of y2 and y3 (saved as cov_y2y3)
'         H(2,4) = cov of y2 and y4 (saved as cov_y2y4)
'         H(3,3) = variance of y3   (saved as var_y3)
'         H(3,4) = cov of y3 and y4 (saved as cov_y3y4)
'         H(4,4) = variance of y4   (saved as var_y4)
' omega = 4 x 4 low triangular 
'  beta = 4 x 4 diagonal
' alpha = 4 x 4 diagonal
'

'change path to program path
%path = @runpath
cd %path 

' load workfile
load intl_fin.wf1

' dependent variables of all series must be continues
series y1 = dlog(sp500)
series y2 = dlog(ftse)
series y3 = dlog(nikkei)
series y4 = dlog(tbond)

' set sample 
' first observation of s1 need to be one or two periods after
' the first observation of s0 
sample s0 3/3/94  8/1/2000
sample s1 3/7/94  8/1/2000

' initialization of parameters and starting values
' change below only to change the specification of model 
smpl s0

'get starting values from univariate GARCH 
equation eq1.arch(m=100,c=1e-5) y1 c 
equation eq2.arch(m=100,c=1e-5) y2 c
equation eq3.arch(m=100,c=1e-5) y3 c
equation eq4.arch(m=100,c=1e-5) y4 c

' declare coef vectors to use in GARCH model
coef(4) mu
 mu(1) = eq1.c(1)
 mu(2) = eq2.c(1)
 mu(3) = eq3.c(1)
 mu(4) = eq4.c(1)

coef(10) omega
 omega(1) = (eq1.c(2))^.5
 omega(2) = 0 
 omega(3) = 0
 omega(4) = eq2.c(2)^.5
 omega(5) = 0
 omega(6) = eq3.c(2)^.5

 omega(8) = eq4.c(2)^.5

coef(4) alpha
 alpha(1) = (eq1.c(3))^.5
 alpha(2) = (eq2.c(3))^.5 
 alpha(3) = (eq3.c(3))^.5 
 alpha(4) = (eq4.c(3))^.5 

coef(4) beta 
 beta(1) = (eq1.c(4))^.5 
 beta(2) = (eq2.c(4))^.5
 beta(3) = (eq3.c(4))^.5
 beta(4) = (eq4.c(4))^.5


' use sample var-cov as starting value of variance-covariance matrix

series cov_y1y2 = @cov(y1-mu(1), y2-mu(2))
series cov_y1y3 = @cov(y1-mu(1), y3-mu(3))
series cov_y1y4 = @cov(y1-mu(1), y4-mu(4))
series cov_y2y3 = @cov(y2-mu(2), y3-mu(3))
series cov_y2y4 = @cov(y2-mu(2), y4-mu(4))
series cov_y3y4 = @cov(y3-mu(3), y4-mu(4))

series var_y1 = @var(y1)
series var_y2 = @var(y2)
series var_y3 = @var(y3)
series var_y4 = @var(y4)

series sqres1 = (y1-mu(1))^2
series sqres2 = (y2-mu(2))^2
series sqres3 = (y3-mu(3))^2
series sqres4 = (y4-mu(4))^2

series res1res2 = (y1-mu(1))*(y2-mu(2))
series res1res3 = (y1-mu(1))*(y3-mu(3))
series res1res4 = (y1-mu(1))*(y4-mu(4))
series res2res3 = (y3-mu(3))*(y2-mu(2))
series res2res4 = (y4-mu(4))*(y2-mu(2))
series res3res4 = (y4-mu(4))*(y3-mu(3))

' constant adjustment for log likelihood
!mlog2pi = 3*log(2*@acos(-1))


' ...........................................................
' LOG LIKELIHOOD
' set up the likelihood 
' 1) open a new blank likelihood object name tvgarch
' 2) specify the log likelihood model by append
' ...........................................................

logl tvgarch

' squared errors and cross errors
tvgarch.append @logl logl
tvgarch.append sqres1 = (y1-mu(1))^2
tvgarch.append sqres2 = (y2-mu(2))^2
tvgarch.append sqres3 = (y3-mu(3))^2
tvgarch.append sqres3 = (y4-mu(4))^2

tvgarch.append res1res2 = (y1-mu(1))*(y2-mu(2))
tvgarch.append res1res3 = (y1-mu(1))*(y3-mu(3))
tvgarch.append res1res4 = (y1-mu(1))*(y4-mu(4))
tvgarch.append res2res3 = (y3-mu(3))*(y2-mu(2))
tvgarch.append res2res4 = (y4-mu(4))*(y2-mu(2))
tvgarch.append res3res4 = (y4-mu(4))*(y3-mu(3))

' variance and covariance series 
tvgarch.append var_y1  =  omega(1)^2 + beta(1)^2*var_y1(-1) + alpha(1)^2*sqres1(-1)
tvgarch.append var_y2  = omega(2)^2+omega(4)^2 + beta(2)^2*var_y2(-1) + alpha(2)^2*sqres2(-1)
tvgarch.append var_y3  = omega(3)^2+omega(5)^2+omega(6)^2 + beta(3)^2*var_y3(-1) + alpha(3)^2*sqres3(-1)

tvgarch.append cov_y1y2 = omega(1)*omega(2) + beta(2)*beta(1)*cov_y1y2(-1) + alpha(2)*alpha(1)*res1res2(-1)
tvgarch.append cov_y1y3 = omega(1)*omega(3) + beta(3)*beta(1)*cov_y1y3(-1) + alpha(3)*alpha(1)*res1res3(-1)
tvgarch.append cov_y2y3 = omega(2)*omega(3) + omega(4)*omega(5) + beta(3)*beta(2)*cov_y2y3(-1) + alpha(3)*alpha(2)*res2res3(-1)

' determinant of the variance-covariance matrix
tvgarch.append deth = var_y1*var_y2*var_y3 - var_y1*cov_y2y3^2-cov_y1y2^2*var_y3+2*cov_y1y2*cov_y2y3*cov_y1y3-cov_y1y3^2*var_y2

' calculate the elements of the inverse of var_cov (H) matrix 
' numbered as vech(inv(H))
tvgarch.append invh1 = (var_y2*var_y3-cov_y2y3^2)/deth
tvgarch.append invh2 = -(cov_y1y2*var_y3-cov_y1y3*cov_y2y3)/deth
tvgarch.append invh3 = (cov_y1y2*cov_y2y3-cov_y1y3*var_y2)/deth
tvgarch.append invh4 = (var_y1*var_y3-cov_y1y3^2)/deth
tvgarch.append invh5 = -(var_y1*cov_y2y3-cov_y1y2*cov_y1y3)/deth
tvgarch.append invh6 = (var_y1*var_y2-cov_y1y2^2)/deth

' log-likelihood series
tvgarch.append logl = -0.5*(!mlog2pi + (invh1*sqres1+invh4*sqres2+invh6*sqres3 +2*invh2*res1res2 +2*invh3*res1res3+2*invh5*res2res3 ) + log(deth))

' remove some of the intermediary series
'tvgarch.append @temp invh1 invh2 invh3 invh4 invh5 invh6 sqres1 sqres2 sqres3 res1res2 res1res3 res2res3 deth

' estimate the model
smpl s1
tvgarch.ml(showopts, m=100, c=1e-5)

' change below to display different output
show tvgarch.output
graph var.line var_y1 var_y2 var_y3
graph cov.line cov_y1y2 cov_y1y3 cov_y2y3
show var
show cov

' LR statistic for univariate vs trivariate
scalar lr = -2*(eq1.@logl + eq2.@logl + eq3.@logl - tvgarch.@logl)
scalar lr_pval = 1 - @cchisq(lr,3)