ode-initval/system.ss
```#lang scheme/base
;;; PLT Scheme Science Collection
;;; ode-initval/system.ss
;;; Copyright (c) 2004-2008 M. Douglas Williams
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 2.1 of the License, or (at your option) any later version.
;;;
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free
;;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
;;; 02111-1307 USA.
;;;
;;; -------------------------------------------------------------------
;;;
;;; This module provides all of the random distributions for the PLT
;;; Science Collection as a single module.
;;;
;;; Version  Date      Description
;;; 2.1.0    06/06/06  Creating separate modules and maling V4.0 changes.
;;;                    (Doug Williams)

;;; Description of a systems of ODEs.
;;;
;;; y' = f(t, y) = dydt(t, y)
;;;
;;; The system is specified by giving the right-hand-side of the
;;; equation and possibly a Jacobian function.
;;;
;;; Some methods require the Jacobian function, which calculated the
;;; matrix dfdy and the vector dfdt.

(provide (all-defined-out))

(define-struct ode-system
(function
jacobian
dimension
params))

;; ode-system-function-eval:
;;   ode-system x real x vector of real x vector of real -> void
(define (ode-system-function-eval ode-system t y dydt)
((ode-system-function ode-system)
t y dydt (ode-system-params ode-system)))

;; ode-system-jacobian-eval:
;;   ode-system x real x vector of real x matrix of real x vector of real -> void
(define (ode-system-jacobian-eval ode-system  t y dfdy dfdt)
((ode-system-jacobian ode-system)
t y dfdy dfdt (ode-system-params ode-system)))
```