Dear all,

sorry for this simple question. What I want to do is to impose a simple parameter constraint. If I want to set two parameters equal, I simply use the same label. However, what if I want to set parameter a = 2*b, so that actually only one parameter is freely estimated?

After searching the archives, the only cumbersome way I came up with is to define two new matrices with a single element but new names, use the mxAlgebra function to multiply by two and then use the mxConstraint function to set the matrices equal. So I did something like that

```
mxMatrix(type = "Full", nrow=1, ncol=1, free=F, values = 0, label="a", name="con_a"),
mxMatrix(type = "Full", nrow=1, ncol=1, free=T, values = 1, label="b", name="con_b"),
mxAlgebra(expression= 2*con_b, name="con"),
mxConstraint("con", "=", "con_a"),
```

But then something goes wrong, and I am not sure why. Do I have to define the elements of both matrices as free? fixed? Is not there a simpler way? This seems overly complicated.

Thank you very much!