Every time I think I know what's going on, suddenly there's another layer of complications.
2017年9月3日星期日
2017年8月31日星期四
Review some Monte Carlo theorems
1.
Suppose the random variable U has a uniform (0,1) distribution.
Let F be a continuous distribution function. Then the random variable X = F^(-1)(U)
has distribution function F.
Note: F(x)=(x-a)/(b-a), for uniform random variable at [a,b] interval. Here F(u)=u.
2.Monte Carlo Integration
generate x1, x2,...,xn from uniform(a,b), then compute Yi = (b - a)g(Xi). Then mean Y is a consistent estimate of the integral
Note: 1. definite integral is a number.
3. Accept-Reject Generation Algorithm
Suppose the random variable U has a uniform (0,1) distribution.
Let F be a continuous distribution function. Then the random variable X = F^(-1)(U)
has distribution function F.
Note: F(x)=(x-a)/(b-a), for uniform random variable at [a,b] interval. Here F(u)=u.
2.Monte Carlo Integration
generate x1, x2,...,xn from uniform(a,b), then compute Yi = (b - a)g(Xi). Then mean Y is a consistent estimate of the integral
Note: 1. definite integral is a number.
3. Accept-Reject Generation Algorithm
2017年8月30日星期三
Difference between indefinite and definite integrals.
Indefinite integrals are functions while definite integrals are numbers. This is quite useful when we calculate Bayesian estimator
2017年8月29日星期二
2017年8月26日星期六
Different likelihoods
Maximum Likelihood
Find β and θ that maximizes L(β, θ|data).
Partial Likelihood
If we can write the likelihood function as:
L(β, θ|data) = L1(β|data) L2(θ|data)
Then we simply maximize L1(β|data).
Profile Likelihood
If we can express θ as a function of β then we replace θ with the corresponding function.
Say, θ = g(β). Then, we maximize:
L(β, g(β)|data)
Marginal Likelihood
We integrate out θ from the likelihood equation by exploiting the fact that we can identify the probability distribution of θ conditional on β.
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