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A Type of New Lower Order Nonconforming Mixed Finite Elements Methods for the Extended Fisher-Kolmogorov Equation
Zhang Houchao, Wang Junjun, Shi Dongyang
Acta mathematica scientia,Series A. 2018, 38 (3):
571-587.
The purpose of this paper is to study the mixed finite element methods with a type of lower order nonconforming finite elements for the extended Fisher-Kolmogorov(EFK) equation. Firstly, a nonconforming mixed finite element scheme is established by splitting the EFK equation into two second order equations through a intermediate variable v=-△u. Some a priori bounds are derived by use of Lyapunov functional, existence and uniqueness for the approximation solutions are also proved. The optimal error estimates for both the primitive solution u and the intermediate variable v in H1-norm are deduced for semi-discrete scheme by use of the above priori bounds and properties of the elements. Furthermore, the superclose properties with order O(h2) are obtained through high accuracy results of the elements. Secondly, a new linearized backward Euler full-discrete scheme is established. The optimal error estimates and superclose results for u and v in H1-norm with orders O(h+τ) and O(h2 +τ) are obtained respectively through the new splitting techniques for consistency errors and nonlinear terms. Here, h, τ are parameter of the subdivision in space and time step. Finally, numerical results are provided to confirm the theoretical analysis. Our analysis provides a new understanding with nonconforming mixed finite element methods to analyze other fourth order initial boundary value problems.
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