data {
  int<lower=1> n_days;
}
parameters {
  real<lower=0, upper=1> mu[n_days];
}
model {
  mu[1]  ~ normal(0.5,0.00001);
  for (i in 2:(n_days))
      mu[i] ~ normal(mu[i - 1], 0.005);

mu[n_days] ~ normal(0.6,0.00001);
}

data {
  int<lower=1> n_days;
}
parameters {
  real<lower=0, upper=1> mu[n_days];
}
model {
  mu[1]  ~ normal(0.5,0.00001);
  for (i in 2:(n_days - 1))
      mu[i] ~ normal(mu[i - 1], 0.005);

mu[n_days] ~ normal(0.6,0.00001);
}