This paper describes a set of interfaces for numerical subroutines. Ty
ping a short (often one-line) description allows one to solve problems
in application domains including fitting, differential equations, min
imization, root finding, and integration. Our approach of ''template-d
riven programming'' makes it easy to build such an interface: a simple
one takes a few hours to construct, while a few days suffice to build
the most complex program we describe.