When creating a model to solve SDP

```
@variable(model, X[1:n,1:n], PSD)
@constraint(model, A*vec(X).==b)
@objective(model, Min, c*vec(X))
```

I got an error

```
ERROR: MethodError: no method matching *(::SparseVector{Int64, Int64}, ::Base.ReshapedArray{VariableRef, 1, Symmetric{VariableRef, Matrix{VariableRef}}, Tuple{Base.MultiplicativeInverses.SignedMultiplicativeInverse{Int64}}})
```

which basically says that I cannot multiply (as in LinearAlgebra.dot) a vector and another Array{VariableRef}.

A quick fix is `sum(c.*vec(X))`

but what is the correct way to write such objective function?