Problem with using ODE solvers

Markthomas — Sat, 07 Nov 2009 19:10:04 -0500

I am trying to run an ODE case usin ode45... the scripts are seen below:
---------------------------------------------code 1------------------------------------------------------------------
function varargout = odefile_V2(t,T,flag,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)

switch flag
    case ''
        varargout{1} = f(t,T,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
    case 'init'
        [varargout{1:3}] = init(tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
end

%--------------------------------------------------------------------------
function dydt = f(t,T,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)

dydt(1) = (-(ET*(T(1)^4-(1200*(1-exp(-t/tau)))^4)+(R1*ET*(T(1)^4-(1200*(1-exp(-t/tau)))^4)+T(1)-T2(t))/R2)/rho1/L1/C1+4*ET*R1*(1200*(1-exp(-t/tau)))^3*((1200/tau)*exp(-t/tau)))/(4*ET*R1*T(1)^3+1);
dydt(2) = (R3*ET*R1*T(1)^4+R3*T(1)+(-R3-R2)*T(2)-R3*ET*R1*(1200*(1-exp(-t/tau)))^4+R2*T(3))/R2/R3/rho2/L2/C2;
dydt(3) = (T(2)-T(3))/R3/rho3/L3/C3;

function [tspan,y0,options] = init(tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)
tspan = [0; 100];
y0 = [300; 300; 300];
options = [];
---------------------------------------------code 2------------------------------------------------------------------
clear; clc; close all
% Material @ Node 0
T0_0 = 300;
% Material @ Node 1
T1_0 = 300;
K1 = 60;
rho1 = 8000;
C1 = 440;
L1 = .07;
% Material @ Node 2
T2_0 = 300;
K2 = 1.4;
rho2 = 1300;
C2 = 1500;
L2 = .04;
% Material @ Node 2
T3_0 = 300;
K3 = 50;
rho3 = 7500;
C3 = 400;
L3 = .02;
%Resistances
R1 = L1/(2*K1);
R2 = R1 + (L2/(2*K2));
R3 = (L2/(2*K2)) + (L3/(2*K3));
% Other Constants
ET = 4e-8;
tau = 50;

[t,T]=ode45('odefile_V2',tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
------------------------------------------------------------------------------------------------------------------------
i keep getting errors and was hoping somebody was able to figure out what is going wrong. I have rewritten the code several times and can't seem to get it to work... any help would be great!

Thanks!
MT

Re: Problem with using ODE solvers

Chris — Sat, 14 Nov 2009 23:40:20 -0500

If I understand this code correctly, then I believe you might have a similar problem since it seems like the ode45 function needs the following arguments.

ode45(function, time span, initial conditions)

However, with your ode45 function:
[t,T]=ode45('odefile_V2',tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);

tau is probably suppose to be the time span, which I think is suppose to be a function.

But, I am still learning the MATLAB, so a lot of your other code still looks too advanced for me.

"Markthomas " <cutonem@clarkson.edu> wrote in message <hd4gmc$amd$1@fred.mathworks.com>...
> I am trying to run an ODE case usin ode45... the scripts are seen below:
> ---------------------------------------------code 1------------------------------------------------------------------
> function varargout = odefile_V2(t,T,flag,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)
>
> switch flag
> case ''
> varargout{1} = f(t,T,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
> case 'init'
> [varargout{1:3}] = init(tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
> end
>
> %--------------------------------------------------------------------------
> function dydt = f(t,T,tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)
>
> dydt(1) = (-(ET*(T(1)^4-(1200*(1-exp(-t/tau)))^4)+(R1*ET*(T(1)^4-(1200*(1-exp(-t/tau)))^4)+T(1)-T2(t))/R2)/rho1/L1/C1+4*ET*R1*(1200*(1-exp(-t/tau)))^3*((1200/tau)*exp(-t/tau)))/(4*ET*R1*T(1)^3+1);
> dydt(2) = (R3*ET*R1*T(1)^4+R3*T(1)+(-R3-R2)*T(2)-R3*ET*R1*(1200*(1-exp(-t/tau)))^4+R2*T(3))/R2/R3/rho2/L2/C2;
> dydt(3) = (T(2)-T(3))/R3/rho3/L3/C3;
>
> function [tspan,y0,options] = init(tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3)
> tspan = [0; 100];
> y0 = [300; 300; 300];
> options = [];
> ---------------------------------------------code 2------------------------------------------------------------------
> clear; clc; close all
> % Material @ Node 0
> T0_0 = 300;
> % Material @ Node 1
> T1_0 = 300;
> K1 = 60;
> rho1 = 8000;
> C1 = 440;
> L1 = .07;
> % Material @ Node 2
> T2_0 = 300;
> K2 = 1.4;
> rho2 = 1300;
> C2 = 1500;
> L2 = .04;
> % Material @ Node 2
> T3_0 = 300;
> K3 = 50;
> rho3 = 7500;
> C3 = 400;
> L3 = .02;
> %Resistances
> R1 = L1/(2*K1);
> R2 = R1 + (L2/(2*K2));
> R3 = (L2/(2*K2)) + (L3/(2*K3));
> % Other Constants
> ET = 4e-8;
> tau = 50;
>
> [t,T]=ode45('odefile_V2',tau,ET,R1,rho1,L1,C1,R3,R2,rho2,L2,C2,rho3,L3,C3);
> ------------------------------------------------------------------------------------------------------------------------
> i keep getting errors and was hoping somebody was able to figure out what is going wrong. I have rewritten the code several times and can't seem to get it to work... any help would be great!
>
> Thanks!
> MT

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Problem with using ODE solvers

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