**Celestial Mechanics on a Graphing Calculator**

## 5. The TI-82 programs

This column used 4 programs written in the TI version of BASIC.
They should be easily convertible to any other form of that
language. In these programs the list `L`_{1}
acts like the 4-component vector `(x,y,v,w)`. The
windows are adjustable inside the programs, and are set for
initial conditions similar to those used in the column. The
input `L`_{1} must be given as a list inside
curly brackets {}. The other inputs requested are `B`
the stopping time, `N` the number of steps, or `M`
the maximum velocity rotation tolerance, as appropriate.
In RK-ADAPT the *sine* of the angle between the
old velocity vector and the new is compared with the
tolerance.
The three programs EULER4, RK and RK-ADAPT all use the
program KSUB as subroutine.

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@ Copyright 2001, American Mathematical Society.