Arow directions
Activation and repression can be distinguished in two ways: by numerically comparing kineticLaws for
two species concentrations, or by symbolically differentiating the kineticLaw and checking whether
the resulting expression is always positive (or always negative). The numerical approach may give
misleading results if the kineticLaw is not monotonic, whereas the symbolic method is more
conservative, but may be very slow in some cases.