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M0nbar :: divisorClassRepresentativeM0nbar(ZZ,HashTable)

divisorClassRepresentativeM0nbar(ZZ,HashTable) -- creates an object of type DivisorClassRepresentativeM0nbar

Synopsis

Description

This function creates an object of type DivisorClassRepresentativeM0nbar from a hash table. Here is a basic example:

i1 : H1=new HashTable from { {{1,3},1}, {{1,4},1} };
i2 : divisorClassRepresentativeM0nbar(6,H1)

o2 = DivisorClassRepresentativeM0nbar{DivisorExpression => HashTable{{1, 3} => 1}}
                                                                     {1, 4} => 1
                                      NumberOfMarkedPoints => 6

o2 : DivisorClassRepresentativeM0nbar

Warning: when you enter a hash table in Macaulay2, if you use a key more than once, the first instance is discarded. Here is an example where the behavior may differ from what you want:

i3 : H=new HashTable from { {{1,3},1}, {{1,4},1}, {{1,3},2}}

o3 = HashTable{{1, 3} => 2}
               {1, 4} => 1

o3 : HashTable

The user probably wanted $\delta_{\{1,3\}} + 2\delta_{\{1,3\}}$ to give $3\delta_{\{1,3\}}$ instead. The moral of the story: if your expression has two terms that are written exactly alike, you could either combine them before you create the input hash table, or input a list instead:

i4 : L= { {{1,3},1}, {{1,4},1}, {{1,3},2}}

o4 = {{{1, 3}, 1}, {{1, 4}, 1}, {{1, 3}, 2}}

o4 : List
i5 : divisorClassRepresentativeM0nbar(6,L)

o5 = DivisorClassRepresentativeM0nbar{DivisorExpression => HashTable{{1, 3} => 3}}
                                                                     {1, 4} => 1
                                      NumberOfMarkedPoints => 6

o5 : DivisorClassRepresentativeM0nbar

For this reason, most users will probably prefer to enter divisors via lists, rather than hash tables.

The function divisorClassRepresentative does the same minimal testing if you enter a hash table that it does if you enter a list. See the documentation for divisorClassRepresentativeM0nbar(ZZ,List).