Vector multiplication in BUGS and JAGS

Question

In R, c(3,1,0) * c(2,0,1) == c(6,0,0). This is not dot product and it's not cross product. First, what is the name for this product, and second, does it work in WinBUGS, OpenBUGS and/or JAGS?

Answer 1

Unlike JAGS, WinBUGS and OpenBUGS does not do this form of vectorization; you have to write a loop, and compute each element 'by hand', as described above.

Answer 2

Martyn Plummer points out that this is implemented in JAGS, which I missed when reading the manual. From Ch 5:

Scalar functions taking scalar arguments are automatically vectorized. They can also be called when the arguments are arrays with conforming dimensions, or scalars. So, for example, the scalar $c$ can be added to the matrix $A$ using

B <- A + c

instead of the more verbose form

D <- dim(A)
for (i in 1:D[1])
  for (j in 1:D[2]) {
    B[i,j] <- A[i,j] + c
  }
}

Answer 3

To do element-wise multiplication you can just make a for loop in those languages and that's it! I've used for loops in WinBUGS with no problems.

Answer 4

Incidentally, element-wise multiplication of two equal length vectors is called the Hadamard product (aka the Schur product).