  This paper describes a user-friendly frontend to a Fortran program that
integrates coupled nonlinear ordinary differential equations. The user
interface is built using the NeXTstep Interface Builder, together with a
public-domain graphical palette for displaying intermediate and final results.
In running the code for a given set of equation parameters the user sees a plot
of the solutions at each stage of the iterative process. In the case of a
successful sequence of iterations, the initially discontinuous curves smooth
out as the scale parameters of the solutions are adjusted to achieve a solution
to the nonlinear equations. If the iterative process goes astray, as it often
does for a poor choice of starting scale parameters, the user has the
opportunity to stop and start over with a better choice, guided by the result
of the previous run. The ease of interaction with the equations also allows the
user to develop an intuition regarding their solutions and to explore the
parameter space for the equations much more quickly.
