Note: the following is a bit outdated…
The following generic package implements in Ada the adaptive-stepsize 4th order Runge-Kutta algorithm, as described by Press (1992). It makes use of the BLAS library, which allows it for example to make use of Altivec on G4 Macs running Mac OS 10.2 or better. The package is made easily reusable by use of the Ada generic mechanism to specify the foating-point precision, and the system of equations to integrate. The package is distributed under the GPL license. Included is a version of the ada_blas package by Duncan Sands, changed to uppercase to work under Mac OS 10.2.
See example.adb for example usage, and rk.ads for a description of the procedure parameters.