I am trying to do some vector arithmetic on an array but unsure of the general syntax that would achieve this. In a very simple form, consider

```
data {
vector[K] p;
}
parameters {
array[K] vector[D] mu;
}
```

As part of my model, I would like to construct the sum mu[k] * p[k] which is a D dimensional vector. How do I do this as efficiently as possible?