function xdot = heater(t,x);
%
%  Dynamics of a stirred tank heater
%  (c) 1994 - B.W. Bequette 
%  8 July 94
%
%  x(1)     =  T  =  temperature in tank
%  x(2)     =  Tj =  temperature in jacket
%  delFj    =        change in jacket flowrate
%  F        =        Tank flowrate
%  Tin      =        Tank inlet temperature
%  Tji      =        Jacket inlet temperature
%  V        =        Tank volume
%  Vj       =        Jacket volume
%  rhocp    =        density*heat capacity
%  rhocpj   =        density*heat capacity,jacket fluid
%
%  parameter and steady-state variable values are:
%
  F     =   1;
  Fjs   =   1.5;
  Ti    =  50;
  Tji   = 200;
  V     =  10;
  Vj    =   1;
  rhocp = 61.3;
  rhocpj= 61.3;
  UA    = 183.9;
%
% revise the following if you want a step change in jacket flow
  delFj =   0;
  Fj = Fjs + delFj;
  T = x(1);
  Tj= x(2);
%
% odes
%
  dTdt = (F/V)*(Ti - T) + UA*(Tj - T)/(V*rhocp);
  dTjdt = (Fj/Vj)*(Tji - Tj) - UA*(Tj - T)/(Vj*rhocpj);
  xdot = [dTdt; dTjdt];

%Figure M5.7a is obtained using the following commands (MATLAB 4.x)
%x0 =
%  124.6525
%  154.9880
% [t,x] = ode45('heater',0,5,x0);
% plot(t,x(:,1))
% 
% for MATLAB 5.x, use
% [t,x] = ode45('heater',[0 5],x0);