A Nodally Bound Preserving Finite Element Method

  • Barrenechea, Gabriel (University of Strathclyde)
  • Georgoulis, Emmanuil (University of Heriot-Watt)
  • Pryer, Tristan (University of Bath)
  • Veeser, Andreas (Universita degli studi di Milano)

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In this talk I will review recent results on positivity-preserving finite element methods. More precisely, I will present a method that enforces bound-preservation (at the degrees of freedom) of the discrete solution. The method is built by first defining an algebraic projection onto the convex closed set of finite element functions that satisfy the bounds given by the solution of the PDE. Then, this projection is hardwired into the definition of the method by writing a discrete problem posed for this projected part of the solution. Since this process is done independently of the shape of the basis functions, and no result on the resulting finite element matrix is used, then the outcome is a finite element function that satisfies the bounds at the degrees of freedom. Another important observation to make is that this approach is related to variational inequalities, and this fact will be exploited in the error analysis. The core of the talk will be devoted to explaining the main idea in the context of linear (and nonlinear) reaction-diffusion equations. Then, I will explain the main difficulties encountered when extending this method to convection-diffusion equations and time-dependent problems.