# dual(MonomialIdeal,List) -- the Alexander dual

## Synopsis

• Function: dual
• Usage:
dual(I,e)
• Inputs:
• I, , a monomial ideal
• e, a list, a list of exponents
• Optional inputs:
• Outputs:
• the Alexander dual of I formed with respect to the monomial whose exponents are listed in e

## Description

The monomial corresponding to e should be divisible by all of the minimal generators of I.

The computation is done by calling the frobby library, written by B. H. Roune; setting gbTrace to a positive value will cause a message to be printed when it is called.