Circle

model
{
	x ~ dunif(-1, 1)
	y ~ dunif(-1, 1)
	O <- 0
	O ~ dbern(constraint)
	constraint <- step(x * x + y * y - 1)
}

Inits list(x = 0, y = 0)

				

Square minus circle

model
{
	x ~ dunif(-1, 1)
	y ~ dunif(-1, 1)
	O <- 1
	O ~ dbern(constraint)
	constraint <- step(x * x + y * y - 1)
}

Inits list(x = 0.99, y = 0.99)

		
Ring

model
{
	x ~ dunif(-1, 1)
	y ~ dunif(-1, 1)
	O1 <- 0
	O1 ~ dbern(constraint1)
	constraint1 <- step(x * x + y * y - 1)	
	O2 <- 1
	O2 ~ dbern(constraint2)
	constraint2 <- step( x * x + y * y - 0.25)
}

Inits list(x = 0.6, y = 0.6)

		
Hollow square

model
{
	x ~ dunif(-1, 1)
	y ~ dunif(-1, 1)
	O <- 0
	O ~ dbern(constraint)
	constraint <- (step(0.5 - abs(x)) * step(0.50 - abs(y)))
}

Inits list(x = 0.75, y = 0.75)

		
Parallelagram

model
{
	x ~ dunif(0, 1)
	y ~ dunif(-1, 1.0)
	O1 <- 1
	O1 ~ dbern(constraint1)
	constraint1 <- step(x + y)
	O2 <- 0
	O2 ~ dbern(constraint2)	
	constraint2 <- step(x + y - 1)
}

Inits list(x = 0.5, y = 0)