Given a list $ML$ of matroids on a common ground set, this method stores the data as a FlagMatroid.
i1 : ML = {uniformMatroid(2,6),matroid completeGraph 4}
o1 = {a matroid of rank 2 on 6 elements, a matroid of rank 3 on 6 elements}
o1 : List
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i2 : FM = flagMatroid(ML)
o2 = a flag matroid with rank sequence {2, 3} on 6 elements
o2 : FlagMatroid
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i3 : isWellDefined FM o3 = true |
For $A$ an $r\times n$ matrix over a field and $L = \{r_1, \ldots, r_k}$ a list of integers, let $M_i$ be the Matroid defined by the columns of the matrix obtained by the first $r_i$ rows of $A$. These matroids form a flag matroid $\mathbf M = \{M_1, \ldots, M_k\}$. This method creates this FlagMatroid.
i4 : A = random(QQ^2,QQ^4)
o4 = | 9/2 9/4 1 3/2 |
| 1/2 1/2 3/4 3/4 |
2 4
o4 : Matrix QQ <--- QQ
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i5 : FM = flagMatroid(A,{1,2})
o5 = a flag matroid with rank sequence {1, 2} on 4 elements
o5 : FlagMatroid
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When a list of matroids is given as input, this method does not check if the flag matroid is well-defined.
The object flagMatroid is a method function.