Quasi-interpolation and a posteriori error analysis in finite element methods
One of the main tools in the proof of residual-based a posteriori error estimates is a quasi-interpolation operator due to Clément. We modify this operator in the setting of a partition of unity with the effect that the approximation error has a local average zero. This results in a new residual-based a posteriori error estimate with a volume contribution which is smaller than in the standard estimate. For an elliptic model problem, we discuss applications to conforming, nonconforming and mixed...
We obtain an existence theorem for the problem (0.1) where the coefficients satisfy a degenerate ellipticity condition and hypotheses weaker than the continuity with respect to the variable .
We prove an existence result for equations of the form where the coefficients satisfy the usual ellipticity conditions and hypotheses weaker than the continuity with respect to the variable . Moreover, we give a counterexample which shows that the problem above may have no solution if the coefficients are supposed only Borel functions
We study the quasilinear elliptic problem with multivalued terms.We consider the Dirichlet problem with a multivalued term appearing in the equation and a problem of Neumann type with a multivalued term appearing in the boundary condition. Our approach is based on Szulkin’s critical point theory for lower semicontinuous energy functionals.