22 research outputs found
Deflation for semismooth equations
Variational inequalities can in general support distinct solutions. In this
paper we study an algorithm for computing distinct solutions of a variational
inequality, without varying the initial guess supplied to the solver. The
central idea is the combination of a semismooth Newton method with a deflation
operator that eliminates known solutions from consideration. Given one root of
a semismooth residual, deflation constructs a new problem for which a
semismooth Newton method will not converge to the known root, even from the
same initial guess. This enables the discovery of other roots. We prove the
effectiveness of the deflation technique under the same assumptions that
guarantee locally superlinear convergence of a semismooth Newton method. We
demonstrate its utility on various finite- and infinite-dimensional examples
drawn from constrained optimization, game theory, economics and solid
mechanics.Comment: 24 pages, 3 figure
A semismooth Newton method with analytical path-following for the -projection onto the Gibbs simplex
An efficient, function-space-based second-order method for the -projection onto the Gibbs-simplex is presented. The method makes use of the theory of semismooth Newton methods in function spaces as well as Moreau-Yosida regularization and techniques from parametric optimization. A path-following technique is considered for the regularization parameter updates. A rigorous first and second-order sensitivity analysis of the value function for the regularized problem is provided to justify the update scheme. The viability of the algorithm is then demonstrated for two applications found in the literature: binary image inpainting and labeled data classification. In both cases, the algorithm exhibits mesh-independent behavior
Optimal control for the thin-film equation: Convergence of a multi-parameter approach to track state constraints avoiding degeneracies
We consider an optimal control problem subject to the thin-film equation
which is deduced from the Navier--Stokes equation. The PDE constraint lacks
well-posedness for general right-hand sides due to possible degeneracies; state
constraints are used to circumvent this problematic issue and to ensure
well-posedness, and the rigorous derivation of necessary optimality conditions
for the optimal control problem is performed. A multi-parameter regularization
is considered which addresses both, the possibly degenerate term in the
equation and the state constraint, and convergence is shown for vanishing
regularization parameters by decoupling both effects. The fully regularized
optimal control problem allows for practical simulations which are provided,
including the control of a dewetting scenario, to evidence the need of the
state constraint, and to motivate proper scalings of involved regularization
and numerical parameters
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A semismooth Newton method with analytical path-following for the H1-projection onto the Gibbs simplex
An efficient, function-space-based second-order method for the
H1-projection onto the Gibbs-simplex is presented. The method makes use of
the theory of semismooth Newton methods in function spaces as well as
Moreau-Yosida regularization and techniques from parametric optimization. A
path-following technique is considered for the regularization parameter
updates. A rigorous first and second-order sensitivity analysis of the value function for the regularized problem is provided to justify the update
scheme. The viability of the algorithm is then demonstrated for two
applications found in the literature: binary image inpainting and labeled
data classification. In both cases, the algorithm exhibits meshindependent
behavior
A PDE-constrained optimization approach for topology optimization of strained photonic devices
Recent studies have demonstrated the potential of using tensile-strained, doped Germanium
as a means of developing an integrated light source for (amongst other things) future microprocessors.
In this work, a multi-material phase-field approach to determine the optimal material
configuration within a so-called Germanium-on-Silicon microbridge is considered. Here, an ``optimal"
configuration is one in which the strain in a predetermined minimal optical cavity within
the Germanium is maximized according to an appropriately chosen objective functional. Due to
manufacturing requirements, the emphasis here is on the cross-section of the device; i.e. a socalled
aperture design. Here, the optimization is modeled as a non-linear optimization problem
with partial differential equation (PDE) and manufacturing constraints. The resulting problem is
analyzed and solved numerically. The theory portion includes a proof of existence of an optimal
topology, differential sensitivity analysis of the displacement with respect to the topology, and the
derivation of first and second-order optimality conditions. For the numerical experiments, an array
of first and second-order solution algorithms in function-space are adapted to the current setting,
tested, and compared. The numerical examples yield designs for which a significant increase in
strain (as compared to an intuitive empirical design) is observed