model 

{
 for (i in 1:n)
     {y[i]~dnorm(x[i],tau.y)
      }

 x0~dnorm(400,0.0001)
 x[1]~dnorm(x0,tau.x)

 for (i in 2:n)
     {x[i]~dnorm(x[i-1],tau.x)
      }

 tau.x~dgamma(1,10)
 tau.y~dgamma(1,10)

 k<- -(tau.y/tau.x+2)
 theta1<-k+sqrt(pow(k,2)-4)
 theta2<-k-sqrt(pow(k,2)-4)
 theta<-max(theta1,theta2)
 sigmasq<- -1/(theta*tau.y)
  }