examples/ode-example-1.ss
```(require (planet "ode-initval.ss" ("williams" "science.plt")))
(require (lib "plot.ss" "plot"))

(define (func t y f params)
(let ((mu (car params))
(y0 (vector-ref y 0))
(y1 (vector-ref y 1)))
(vector-set! f 0 y1)
(vector-set! f 1 (- (- y0) (* mu y1 (- (* y0 y0) 1.0))))))

(define (main)
(let* ((type rk4-ode-type)
(step (make-ode-step type 2))
(mu 10.0)
(system (make-ode-system func #f 2 (list mu)))
(t 0.0)
(t1 100.0)
(h 1.0e-2)
(y #(1.0 0.0))
(y-err (make-vector 2))
(dydt-in (make-vector 2))
(dydt-out (make-vector 2))
(y0-values '())
(y1-values '()))
(ode-system-function-eval system t y dydt-in)
(let loop ()
(if (< t t1)
(begin
(ode-step-apply step t h
y y-err
dydt-in
dydt-out
system)
;(printf "~a ~a ~a~n" t (vector-ref y 0) (vector-ref y 1))
(set! y0-values (cons (vector t (vector-ref y 0)) y0-values))
(set! y1-values (cons (vector t (vector-ref y 1)) y1-values))
(vector-set! dydt-in 0 (vector-ref dydt-out 0))
(vector-set! dydt-in 1 (vector-ref dydt-out 1))
(set! t (+ t h))
(loop))))
(printf "~a~n" (plot (points (reverse y0-values))
(x-min 0.0)
(x-max 100.0)
(y-min -2.0)
(y-max 2.0)))
(printf "~a~n" (plot (points (reverse y1-values))
(x-min 0.0)
(x-max 100.0)))
))

(main)```