All Runge–Kutta methods mentioned up to now are explicit methods. Explicit Runge–Kutta methods are generally unsuitable for the solution of stiff equations because their region of absolute stability is small in particular, it is bounded.[14] This issue is especially important in the solution of partial differential equations.-All Runge–Kutta methods mentioned up to now are explicit methods. Explicit Runge–Kutta methods are generally unsuitable for the solution of stiff equations because their region of absolute stability is small　in particular, it is bounded.[14] This issue is especially important in the solution of partial differential equations.