Stan functions work on Eigen::Matrix but not on Eigen::Map. The error occurs for examplew ith `elt_multiply`

, with the following message:

```
/stan/math/prim/mat/fun/elt_multiply.hpp:25:1: note: candidate template
ignored: could not match 'Matrix' against 'Map'
elt_multiply(const Eigen::Matrix<T1, R, C>& m1,
```

But in some cases, it could be handy to use Stan functions directly on `Map`

. Is there a good workaround this, that doesn’t involve creating a new Matrix – and essentially duplicating the object?

**Edit**: how expensive is it actually to duplicate a matrix?