dual: Calculate the dual
In MichaelHoltonPrice/yada: Yet Another Demographic Analysis package

For an overview of combinadics and the dual see [yada::comb]. To calculate the dual, the number of elements that can be chosen, num_elements, must be known. It is either input directly or determined from N and k, which are input. In total, therefore, there are two valid inputs patterns for the three optional inputs num_elements, N, and k: specify numElements or specify both N and k. If all three optional inputs are given, N and k are ignored.

1	dual(m, num_elements = NA, N = NA, k = NA)

`m`	The lexical index of each unique choice (starting from 0)
`num_elements`	The number of things that can be chosen (default: NA, not used)
`N`	The number of unique things (default: NA, not used)
`k`	The number of things to choose out of N total things (default: NA, not used) return The dual, d (see details for [yada::comb]
`d`	The dual(see details)
`e`	The element (a vector; see details)