4 Exact solution for reversibly coupled three species chain Systems of linear differential equations having constant coefficients are known to generally have solutions in exact arithmetic but are perhaps too tedious to be worth the effort in complex network applications. Nonetheless, they can be advantageous for simpler systems containing perhaps three or four species . In , the coupled system of three species is tackled by computing e At in exact arithmetic (via Putzer's algorithm and verified by Laplace transforms) for a 2 × 2 matrix of constants. The solution is a bit tedious to be repeated here but it is useful to outline what was done and demonstrate a third companion method of great flexibility when one employs a CAS, such as the Texas Instruments TI-Nspire calculator, an indispensable tool for electric circuit analysis.