Rev Language Reference


A move to scale a single continuous value by multiplying by a value drawn from a Gamma(lambda,1) distribution. Lambda is the tuning parameter that controls the size of the proposals.


mvGammaScale(RealPos x, RealPos lambda, Bool tune, RealPos weight, Probability tuneTarget)


x : RealPos (<stochastic> pass by reference)
The variable this move operates on.
lambda : RealPos (pass by value)
The strength of the proposal.
Default : 1
tune : Bool (pass by value)
Should we tune lambda during burnin?
Default : TRUE
weight : RealPos (pass by value)
The weight how often on average this move will be used per iteration.
Default : 1
tuneTarget : Probability (pass by value)
The acceptance probability targeted by auto-tuning.
Default : 0.44


# Here is a simple example for conducting MCMC on the mean and sd of a Normal distribution.

# Uniform(0,1) priors on the mean and sd
mean ~ dnUnif(0,1)
sd ~ dnUnif(0,1)

# Dummy data (will not actually be analyzed)
data <- v(0.4,0.5,0.6)

# Clamping data
for (i in 1:data.size()){ outcomes[i] ~ dnNorm(mean,sd); outcomes[i].clamp(data[i]) }

# Initializing move and monitor counters
mvi = 1
mni = 1

# Adding Gamma scale moves for the mean and sd (THIS MOVE IS HERE)
moves[mvi++] = mvGammaScale(mean)
moves[mvi++] = mvGammaScale(sd)

# Instantiating the model
mymodel = model(outcomes)

# Adding screen monitor for the mean
monitors[mni++] = mnScreen(mean, printgen=1000)

# Creating MCMC object
mymcmc = mcmc(mymodel, moves, monitors)

# Running MCMC under the prior,underPrior=TRUE);

See Also