Projections onto convex sets and Lp-quasi-contractivity of semigroups
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- Nittka, R. Arch. Math. (2012) 98: 341. doi:10.1007/s00013-012-0374-2
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Based on a simple geometric description of orthogonal projections onto closed, convex sets we find an implicit formula for the L2-projection onto the Lp-unit ball. This allows us to to prove the Lp-quasi-contractivity of semigroups generated by linear elliptic operators and quasi-linear operators of q-Laplace-type in a simple way.