## Outer Product of Vectors

## Usage

    outer(x, y, FUN = "*", ...)
    x %o% y

## Arguments

`x` | a vector.
`y` | a vector.
`FUN` | a function to use on the outer products, it may be a quoted string.
`...` | optional arguments to be passed to `fun`.

## Description

The outer product of the vectors `x` and `y` is the matrix `A` with elements `A[i, j] = FUN(x[i], y[j], ...)`. `FUN` must be a function which expects at least two arguments and which operates elementwise on arrays.

This needs to be extended to taking arrays of arbitrary dimension for `x` and `y` and returns an array of dimension `c(dim(x), dim(y))`.

`%o%` is an `.Alias` for `outer` (where `FUN` cannot be changed from `"*"`.

## Examples

    outer(1:5, 1:5, "+")
    all(outer(1:5, 1:5) == 1:5 %o% 1:5)

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