todo

开放gsl矩阵运算

* The asymptotic behavior of the secondary functions (sec, csc, cot,
etc) can overflow because of expressions like cosh(x) / D , where D =
cosh^2 which is computed prior to the division.  This should by
special casing "small" vs "large" arguments as has been done for the
sin,cos,tan versions.

* Perhaps there is something useful in LCY65 L. A. Lyusternik,
O. A. Chervonenkis, and A. R. Yanpol'skii, Handbook for computing
elementary functions, International Series of Monographs in Pure and
Applied Mathematics, vol. 76, Pergamon Press, Oxford, 1965.