`X`

and `Y`

must be suitable arguments for `FUN`

. Each
will be extended by `rep`

to length the products of the
lengths of `X`

and `Y`

before `FUN`

is called.

`FUN`

is called with these two extended vectors as arguments
(plus any arguments in `…`

). It must be a vectorized
function (or the name of one) expecting at least two arguments and
returning a value with the same length as the first (and the second).

Where they exist, the [dim]names of `X`

and `Y`

will be
copied to the answer, and a dimension assigned which is the
concatenation of the dimensions of `X`

and `Y`

(or lengths
if dimensions do not exist).

`FUN = "*"`

is handled as a special case *via*
`as.vector(X) %*% t(as.vector(Y))`

, and is intended only for
numeric vectors and arrays.

`%o%`

is binary operator providing a wrapper for
`outer(x, y, "*")`

.