# Semismoothness of spectral functions

Qi, Houduo and Yang, Xiaoqi Qi
(2004)
Semismoothness of spectral functions.
*SIAM Journal on Matrix Analysis and Applications*, 25, (3), 784-803. (doi:10.1137/S0895479802417921).

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## Description/Abstract

Any spectral function can be written as a composition of a symmetric function $f: \rn \mapsto \Re$ and the eigenvalue function $\lambda(\cdot): \s \mapsto \rn$, often denoted by $(f \circ \lambda)$, where $\s$ is the subspace of n × n symmetric matrices. In this paper, we present some nonsmooth analysis for such spectral functions. Our main results are (a) $(f \circ \lambda)$ is directionally differentiable if f is semidifferentiable, (b) $(f \circ \lambda)$ is LC 1 if and only if f is LC 1, and (c) $(f \circ \lambda)$ is SC 1 if and only if f is SC 1. Result (a) is complementary to a known (negative) fact that $(f \circ \lambda)$ might not be directionally differentiable if f is directionally differentiable only. Results (b) and (c) are particularly useful for the solution of LC 1 and SC 1 minimization problems which often can be solved by fast (generalized) Newton methods. Our analysis makes use of recent results on continuously differentiable spectral functions as well as on nonsmooth symmetric--matrix-valued functions.

Item Type: | Article |
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ISSNs: | 0895-4798 (print) |

Related URLs: | |

Keywords: | symmetric function, spectral function, nonsmooth analysis, semismooth function |

Subjects: | Q Science > QA Mathematics |

Divisions: | University Structure - Pre August 2011 > School of Mathematics > Operational Research |

ePrint ID: | 29647 |

Date Deposited: | 12 May 2006 |

Last Modified: | 27 Mar 2014 18:18 |

Contact Email Address: | hdqi@soton.ac.uk |

URI: | http://eprints.soton.ac.uk/id/eprint/29647 |

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