Page 268
% make up an m-file, chemRate.m, with
%   function xprime = chemRate(t,x);
%   k=1; a0=2; b0=3; x0=0.5;
%   xprime = k*(a0+x0-x)*(b0+x0-x);
x0=0.5;
[t,x]=ode23('chemRate',[0 4],x0);
plot(t,x)