Convexity properties of the condition number
We define in the space of n×m matrices of rank n, n ≤ m, the condition Riemannian structure as follows: For a given matrix A the tangent space at A is equipped with the Hermitian inner product obtained by multiplying the usual Frobenius inner product by the inverse of the square of the smallest sing...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2010 |
| País: | España |
| Institución: | Universidad de Cantabria (UC) |
| Repositorio: | UCrea Repositorio Abierto de la Universidad de Cantabria |
| Idioma: | inglés |
| OAI Identifier: | oai:repositorio.unican.es:10902/3208 |
| Acceso en línea: | http://hdl.handle.net/10902/3208 |
| Access Level: | acceso abierto |
| Palabra clave: | Condition number Geodesic Log-convexity Riemannian geometry Linear group |
| Sumario: | We define in the space of n×m matrices of rank n, n ≤ m, the condition Riemannian structure as follows: For a given matrix A the tangent space at A is equipped with the Hermitian inner product obtained by multiplying the usual Frobenius inner product by the inverse of the square of the smallest singular value of A denoted σn(A). When this smallest singular value has multiplicity 1, the function A → log(σn(A)−2) is a convex function with respect to the condition Riemannian structure that is t → log(σn(A(t))−2) is convex, in the usual sense for any geodesic A(t). In a more abstract setting, a function α defined on a Riemannian manifold (M, , ) is said to be self-convex when log α(γ(t)) is convex for any geodesic in (M, α , ). Necessary and sufficient conditions for self-convexity are given when α is C2. When α(x) = d(x,N)−2, where d(x,N) is the distance from x to a C2 submanifold N ⊂Rj, we prove that α is self-convex when restricted to the largest open set of points x where there is a unique closest point in N to x. We also show, using this more general notion, that the square of the condition number A F /σn(A) is self-convex in projective space and the solution variety. |
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