ODE solvers - passing parameters

trange = [0 120];
Cin = [5.1 3.1 387.05];
%Q=0;
[t,c] = ode45(@simul_dif, trange, Cin);

My function is,
function f = simul_dif(t,c)

    k1 = 3.58*10^8;
    k2 = 2.08*10^7;
    E1DR = 9758.3;
    E2DR = 9758.3;
    dHr = 78;
    A = 0.5;
    h = 1;
    Q=100;

    k11 = (k1*exp(-E1DR/c(3)));
    k21 = (k2*exp(-E2DR/c(3)));
    rho = 934.2;
    Cp = 2;
    
    f(1,1) = ((-dHr/(rho*Cp)) * ((k11*c(1))-(k21*c(2))))+(Q/(A*h*rho*Cp));
    f(2,1) = (-k11*c(1))+(k21*c(2));
    f(3,1) = (k11*c(1))-(k21*c(2));

end

What is need to know that how to send a contant Q value from command window to the function instead of define it in the function.

Answer 1

[Star Strider]

It is actually a bit more involved than simply passing parameters when you are using the function with any of the ODE solvers (ode45 specifically here).

The function declaration must be:

function f = simul_dif(t,c,Q)

and the call to it in ode45 must be:

[t,c] = ode45(@(t,c)simul_dif(t,c,Q), trange, Cin);

With both of those changes, it will work.

There are additional considerations if you are defining ‘Q’ as individual elements of a vector in a loop.

[Jamba wumbo]

Hello Star Strider,

Could you help me to check my ode code? because it seems that my code has a NaN value.

Any little help would be appreciated. Thankyou very much. Here is the link ODE Problem

Best Regard,

Hadi

[Walter Roberson]

I am not getting any NaN when I make the obvious changes to your code.

trange = [0 120];
Cin = [5.1 3.1 387.05];
Q = 100;
[t,c] = ode45(@(t,c)simul_dif(t,c,Q), trange, Cin);

function f = simul_dif(t,c,Q)

    k1 = 3.58*10^8;
    k2 = 2.08*10^7;
    E1DR = 9758.3;
    E2DR = 9758.3;
    dHr = 78;
    A = 0.5;
    h = 1;
 

    k11 = (k1*exp(-E1DR/c(3)));
    k21 = (k2*exp(-E2DR/c(3)));
    rho = 934.2;
    Cp = 2;
    
    f(1,1) = ((-dHr/(rho*Cp)) * ((k11*c(1))-(k21*c(2))))+(Q/(A*h*rho*Cp));
    f(2,1) = (-k11*c(1))+(k21*c(2));
    f(3,1) = (k11*c(1))-(k21*c(2));

end

[Star Strider]

Walter — Thank you.

Answer 2

[Stephan]

https://de.mathworks.com/help/optim/ug/passing-extra-parameters.html

[Daz]

Thank you.