Realization space dimension

The Krull dimension of the characteristic-zero realization space. The stored saturated realization space over $\mathbb Z$ is base-changed to $\mathbb Q$ and its dimension is taken. The value $-1$ means the space is empty over $\mathbb Q$, i.e. the matroid is not realizable in characteristic 0. Because a reference basis is normalized to the identity, this is the dimension after dividing out the projective symmetries.

Compare expected dimension, a combinatorial prediction.