## OU ̲ #####
require(stats4)
require(sde)

OU.lik <- function(theta1, theta2, theta3){   # Ȼ
  n <- length(X)
  dt <- deltat(X)
  -sum(dcOU(X[2:n], dt, X[1:(n-1)], c(theta1,theta2,theta3), log=TRUE))  # dcOU Ǵݺ
 }


set.seed(123)

X <- sde.sim(model="OU", theta=c(3,1,2), N=1000, delta=1)  # 


fit <- mle(OU.lik, start=list(theta1=1, theta2=0.5, theta3=1), 
      method="L-BFGS-B", lower=c(-Inf,0,0))
summary(fit)