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求常微分方程的数值解 ode45方法的源代码怎么看懂呢？四百多行 如何理解这些代码的核心思想 以方便未来自己使用呢？求大神指点迷津 感激不尽

function varargout = ode45(ode,tspan,y0,options,varargin)

%ODE45 Solve non-stiff differential equations, medium order method.

% [TOUT,YOUT] = ODE45(ODEFUN,TSPAN,Y0) with TSPAN = [T0 TFINAL] integrates

% the system of differential equations y' = f(t,y) from time T0 to TFINAL

% with initial conditions Y0. ODEFUN is a function handle. For a scalar T

% and a vector Y, ODEFUN(T,Y) must return a column vector corresponding

% to f(t,y). Each row in the solution array YOUT corresponds to a time

% returned in the column vector TOUT. To obtain solutions at specific

% times T0,T1,...,TFINAL (all increasing or all decreasing), use TSPAN =

% [T0 T1 ... TFINAL].

%

% [TOUT,YOUT] = ODE45(ODEFUN,TSPAN,Y0,OPTIONS) solves as above with default

% integration properties replaced by values in OPTIONS, an argument created

% with the ODESET function. See ODESET for details. Commonly used options

% are scalar relative error tolerance 'RelTol' (1e-3 by default) and vector

% of absolute error tolerances 'AbsTol' (all components 1e-6 by default).

% If certain components of the solution must be non-negative, use

% ODESET to set the 'NonNegative' property to the indices of these

% components.

%

% ODE45 can solve problems M(t,y)*y' = f(t,y) with mass matrix M that is

% nonsingular. Use ODESET to set the 'Mass' property to a function handle

% MASS if MASS(T,Y) returns the value of the mass matrix. If the mass matrix

% is constant, the matrix can be used as the value of the 'Mass' option. If

% the mass matrix does not depend on the state variable Y and the function

% MASS is to be called with one input argument T, set 'MStateDependence' to

% 'none'. ODE15S and ODE23T can solve problems with singular mass matrices