 Relative-error approximation for minimization

For a minimization problem with positive optimum, this convention measures the relative excess $(\mathrm{ALG}-\mathrm{OPT})/\mathrm{OPT}$. An epsilon-approximation always returns a feasible solution with excess at most $\epsilon$. A multiplicative-ratio convention instead reports $1+\epsilon$. State the convention explicitly rather than treating these two numbers as interchangeable.