Scalar-Matrix multiplication

@nhuurre, that’s not quite what I’m describing. So with days excluded for simplicity, the one-hot nature of returns the following arrays:

// X      * C                + X       *  B
[1,0,0] * [[c11, c12, c13],  + [1,0,0] * [[b11, b12, b13],  
           [c21, c22, c23],               [b21, b22, b23],
           [c21, c22, c23]]               [b31, b32, b33]]
= [c11, c12, c13] + [b11, b12, b13] 

I simply want to scale every element in X*B by the same scalar value:

days * [b11, b12, b13] = [days*b11, days*b12, days*b13]

This is a trivial task in Numpy; I’m not sure I understand why it’s not intuitive with Stan.

What I want with days included is: X*C + days * X*B* where daysscales every vector element inX*B`.

Hopefully this makes sense!