b = regCheck E
"For a toric vector bundle in Kaneyama's description, the regularity condition means that for every pair of maximal cones $\sigma_1,\sigma_2$intersecting in a common codimensionone face, the two sets of degrees $d_1,d_2$ and the transition matrix $A_{1,2}$ fulfil the regularity condition. I.e. for every $i$ and $j$ we have that either the $(i,j)$ entry of the matrix $A_{1,2}$ is $0$ or the difference of the $i$th degree vector of $d_1$ of $\sigma_1$ and the $j$th degree vector of $d_2$ of $\sigma_2$ is in the dual cone of the intersection of $\sigma_1$ and $\sigma_2$."
Note that this is only necessary for toric vector bundles generated 'by hand' using addBaseChange and addDegrees, since bundles generated for example by tangentBundle satisfy the condition automatically.


The object regCheck is a method function.