2,034 research outputs found
Geometric approach to Fletcher's ideal penalty function
Original article can be found at: www.springerlink.com Copyright Springer. [Originally produced as UH Technical Report 280, 1993]In this note, we derive a geometric formulation of an ideal penalty function for equality constrained problems. This differentiable penalty function requires no parameter estimation or adjustment, has numerical conditioning similar to that of the target function from which it is constructed, and also has the desirable property that the strict second-order constrained minima of the target function are precisely those strict second-order unconstrained minima of the penalty function which satisfy the constraints. Such a penalty function can be used to establish termination properties for algorithms which avoid ill-conditioned steps. Numerical values for the penalty function and its derivatives can be calculated efficiently using automatic differentiation techniques.Peer reviewe
Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsOF
An optimally doped iron-based superconductor LaFeAsOF with
K has been studied by inelastic powder neutron scattering. The
magnetic excitation at \AA is enhanced below , leading to
a peak at meV as the resonance mode, in addition to the
formation of a gap at low energy below the crossover energy . The peak energy at \AA corresponds to in
good agreement with the other values of resonance mode observed in the various
iron-based superconductors, even in the high- cuprates. Although the
phonon density of states has a peak at the same energy as the resonance mode in
the present superconductor, the -dependence is consistent with the resonance
being of predominately magnetic origin.Comment: 4 pages, 5 Postscript figure
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