  The Turing completeness of continuous chemical reaction networks (CRNs)
states that any computable real function can be computed by a continuous CRN on
a finite set of molecular species, possibly restricted to elementary reactions,
i.e. with at most two reactants and mass action law kinetics. In this paper, we
introduce a notion of online analog computation for the CRNs that stabilize the
concentration of their output species to the result of some function of the
concentration values of their input species, whatever changes are operated on
the inputs during the computation. We prove that the set of real functions
stabilized by a CRN with mass action law kinetics is precisely the set of real
algebraic functions.
