#
#An implementation of Ljung-Box.
#It assumes that tsx is a vector or time series. 
#The number of lags parameter is k.
#

myLB<-function(tsx,k){
Tx<-length(tsx);
weight<-rep(0,k);
for(j in 1:k){weight[j]<-1/(Tx-j)};
rho<-acf(tsx, plot=F)$acf[2:(k+1)]; 
wrhosq<-rho^2*weight;
value<-Tx*(Tx+2)*sum(wrhosq);
return(value)
}