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STA120
Worksheet 13 Piero Lorenzini, Stefan Willi Problem 31 (Monte Carlo integration) Estimate the volume of the unit ball in d = 2, 3, . . . , 10 dimensions and compare it to the exact value . What do you notice? Hint : You may adapt the RCode 14.2 from the script. Problem 32 (Rejection sampling 1) We want to draw a sample from a distribution with a density proportional to y(1 − y)(y + 1) for y ∈ [0, 1], i.e. fY (y) ∝ y(1− y)(y + 1). Use fZ(y) = I0≤y≤1(y) = { 1 if 0 ≤ y ≤ 1 0 otherwise as proposal density and draw 100’000 realizations of the density above with a rejection sampling approach. Problem 33 (Rejection sampling 2 – difficult) A random variable X has a Laplace distribution with parameters µ ∈ R and λ > 0 if its density is of the form fX(x) = 1 2λ exp ( −|x− µ| λ ) . (a) Draw 1000 realizations of a Laplace distribution with parameters µ = 0 and λ = 1 with a rejection sampling approach. Hint : For the proposal density you can use the density of the t-distribution with 1 degree of freedom. (b) Propose an intuitive alternative sampling approach based on rexp().