NUTSアルゴリズムにバグがあると聞いて

HMCvsNUTStest.R

model <- '
parameters {
  vector[2] z;
}

model{
  matrix[2,2] sigma;
  vector[2] mu;

  mu[1] <- 0.0;
  mu[2] <- 3.0;
  sigma[1][1] <- 1.0 * 1.0;
  sigma[1][2] <- 0.5 * 1.0 * 2.0;
  sigma[2][1] <- 0.5 * 1.0 * 2.0;
  sigma[2][2] <- 2.0 * 2.0;

  z ~ multi_normal(mu, sigma);
}
'

testing.model <- stan_model(model_code=model)
fit1 <- sampling(testing.model,iter=1000000,warmup=100000,algorithm="HMC")
fit2 <- sampling(testing.model,iter=1000000,warmup=100000,algorithm="NUTS")

print(fit1)
print(fit2)