How to solve Two coupled ODE problem

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0 个投票

hello all,

actually, i have some problem about to solve two coupled ODE that are dependent on each other. if u all have time can u give me some guide about to coding with two coupled equations problem below and plot the graph :-

   function dydt = odefun1(t,y,Aq,Bq,Cq,Ay,By,Cy)
A=1;
B=2;
C=1;
D=3;
E=1;
F=1;
h=1;    
Aq=y(1);
Bq=y(2);
Ay=y(3);
By=y(4);
dydt = zeros(4,1);
dydt(1) = F*dydt(2)-D*Bq-E*Aq;
dydt(2) = (C*Aq-B*By-h*Ay)/A;
dydt = [dydt(1) ; dydt(2) ];
t_start = 0;
t_end   = 10;  %final time in seconds.
%time_span =[ t_start t_end];
time_span =t_start:0.09:t_end;
initial_position = 0;
initial_speed    = 0;
x0 = [initial_position  initial_speed];
[t,y]=ode45(@odefun1,time_span,x0);
    plot(t,y(:,1));
    hold on;
    plot(t,y(:,2));
end

hope u all can answer this question.. thank you in advance. best regards, azam

2 个评论
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James Tursa 2016-9-22

编辑：James Tursa 2016-9-22

If y is a 4-element vector, why are you building a dydt vector that has only 2 elements? If dydt(1) depends on dydt(2), why aren't you calculating dydt(2) before you calculate dydt(1)?

Azam Axel 2016-9-26

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Thank you James for your answer,but i'm still having the same problem though. i changed my code as shown below. no error but cannot produce the graph instead. can u guide me with example code. very appreciate if u can answer this.. tq

 function dydt = odefun1(t,y,Aq,Bq,Cq,Ay,By,Cy)
  A=1;
  B=2;
  C=1;
  D=3;
  E=1;
  F=1;
  h=1;  
Aq=y(1);
Bq=y(2);
Ay=y(3);
By=y(4);
dydt = zeros(4,1);
dydt(1) = (C*Aq-B*By-h*Ay)/A;
dydt(2) = F*dydt(1)-D*Bq-E*Aq;
t_start = 0;
t_end   = 10;  %final time in seconds.
 %time_span =[ t_start t_end];
  time_span =t_start:0.09:t_end;
initial_position = 0;
initial_speed    = 0;
x0 = [initial_position  initial_speed];
[t,y]=ode45(@odefun1,time_span,x0);
    plot(t,y(:,1));
    hold on;
    end