## The expected proportion of draws from component 1.
alpha = 0.05

## The variance of component 1.
tau2 = 100

## The variance of component 2.
sig2 = 1

## A 1000x50 array of iid true/false values in which each entry has
## probability alpha of being true.
A = array((runif(1000*50) < alpha), c(1000,50))

## The component 1 draws.
B = array(sqrt(tau2)*rnorm(50*1000), c(1000,50))

## The component 2 draws.
C = array(sqrt(sig2)*rnorm(50*1000), c(1000,50))

## These are the contaminated normal draws.
X = A*B + (1-A)*C