Accumulated log probability with reduce_sum

Hello all,
After reading the release notes of Stan 2.25 (!!) I am suddenly unsure if I am using reduce_sum correctly.
For every reduce_sum transition, I declare the accumulated log probability (lp) to be 0 - lp=0 and accumulate it using lp += .... until I return it. Please see the simplified example below:

functions {
    real partial_sum(.....) {
      real lp = 0;
      lp += normal_lpdf(...);
      lp += bernoulli_lpmf(...);
      lp += wiener_lpdf(...);
      .
      .
      return lp;
}
}
    .
    .
    .
model {
  target += reduce_sum(partial_sum, .......);
} 

Is this correct? Or should I pass target += into reduce_sum? Or am I completely off?

Thank you!

It’s correct the way you do it.

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Thank you!