This module offers algorithms for the numerical integration of simultaneous differential equations of the form dY/dt = F(t,Y) where Y is an array, or a hash, of variables whose initial values Y(0) are known; and F is a function known from the dynamics of the problem. Three main algorithms are offered. rk2 is Heun's 2nd-order Runge-Kutta algorithm, which is relatively imprecise, but does have a large range of stability which might be useful in some problems. rk4 is Merson's 4th-order Runge-Kutta algorithm, which should be the normal choice in situations where the step-size must be specified. rk_auto uses Merson's 4th-order Runge-Kutta algorithm to adjust the step-size automatically to achieve a specified precision; this saves much fiddling around trying to choose a good step-size, and much CPU time by automatically increasing the step-size when the solution is changing only slowly. Perl is not the right language for high-end numerical integration like global weather simulation, colliding galaxies and so on, but as Gear says, "Many equations that are solved on digital computers can be classified as trivial by the fact that even with an inefficient method of solution, little computer time is used. Economics then dictates that the best method is the one that minimises the human time of preparation of the program." The Lua version runs much faster. This module should be helpful in solving systems of differential equations which arise within a Perl context, such as economic, financial, demographic or ecological modelling, mechanical or process dynamics, etc. Also included are call-compatible translations into JavaScript and Lua. To install: perl Makefile.PL make make test make install For up-to-date source, see Peter J Billam