说明：  奇异值分解算法代码，可用来求取非正定方程组。
(Credits: Ian Kay, Canadian Geological Survey, Ottawa, Ontario 1999. This is a translation in C from an code written in Fortran that appeared in NETLIB, EISPACK, and SLATEC collections that was itself a translation from an original Algol code that appeared in: Golub, G. and C. Reinsch (1971) Handbook for automatic computation II, linear algebra, p 134-151. SpringerVerlag, New York. See also discussions of a similar code in Numerical Recipes in C. svd_sort: Nils Maercklin, GeoForschungsZentrum (GFZ) Potsdam, Germany, 2001. )