For a general network species i may be coupled to other species thus A ii =j k ij where the summation is over all species j coupled to species i. The constant k ji stands alone at row i column j so that A ij = k ji . Likewise A jj =i k ji and A ji = k ij . If we model i and j as irreversibly coupled i kij --→ j the above considerations apply using k ji = 0. Construction of A in MATLAB can be performed by preconstructing a matrix {k ij } of rate constants. When k ij is encountered in a traversal make the assignments