code: private void ensureVarTensor() {
          if (vt == null) {
              log.warn("Generating VarTensor for a GlobalFactor. This should only ever be done during testing.");
              vt = BruteForceInferencer.safeNewVarTensor(s, f);
              if (fillVal != null) {
                  vt.fill(fillVal);
              }
          }
      }
docs: Ensures that the VarTensor is loaded.