f = filtration E
For each ray of the fan there is a filtration matrix. If the bundle has rank $k$ then this is a one row matrix over ZZ with $k$ entries. This defines the filtration on the corresponding base matrix (see base) such that the $j$th filtration is generated by all columns of the base matrix for which the entry in the same column of the filtration matrix is less or equal to $j$.


So in this example for each ray the first column of the basis appears at 1 and the second at 0.
The object filtration is a method function.