stiff equation meaning in English

病态方程
刚性方程

Precise time integration algorithm of stiff equation in nonlinear dynamic system
非线性动力系统刚性方程精细时程积分法
The arbitrary order explicit precise time integration method for stiff equations
任意阶显式精细积分多步法在刚性方程中的应用研究
Applied the precise integration method to solve stiff equations and nonlinear equations , and improved the method from explicit and implicit aspects . it found that the exact solution of some differential equations may be obtained , and always stable absolutely
将之应用于刚性方程及非线性方程的求解中，并对非线性方程的求解从显式和隐式两个方面给出了改进措施，得出：使用精细积分法可以给出某些微分方程的精确解，且绝对稳定。