Pr4oblem with an ODE 45 " not enough input arguments"

I have problem withis system of ode , this is onlya part of the code

N.B I have the latest version of MatLab.

Thanks for your help

Nt=150 
m_ox=0.7;
m_ox=m_ox.*ones(1,Nt);

r_dot=0.0006
m_dot_pr=1.7 ;
v_cham=1*10^(3);
m_fuel= 15.*ones(1,Nt);
burn_time=50;
t=linspace(0,burn_time,Nt)
C=((m_dot_fuel+m_ox-m_dot_pr)./(v_cham)) ;


A=((4*r_dot)./Dp_t);

y1_0=zeros(Nt,1);
y1_0=y1_0(:);
t=t(:);



y2_0=rho_ox_0.*ones(1,Nt);
y2_0=y2_0(:);
y_0=[y1_0,y2_0];



[t_sol,y_sol]=ode45(@(t,y1,y2)zero_dmodelcc(C,A,y1,y2,t,v_cham,m_dot_pr,m_ox),t,y_0);


function dy=zero_dmodelcc(C,A,y1,y2,t,v_cham,m_dot_pr,m_ox)
y=[y1;y2];
v_cham=v_cham(:);

m_ox=m_ox(:);
C=C(:);
A=A(:);
dy1 =C-(y1.*A);
dy1=dy1(:);




dy2=((y1.*m_ox)./(v_cham))+y2.*(A-m_dot_pr);
dy2=dy2(:);
dy=[dy1,dy2];
end 

Answer 1

[Bjorn Gustavsson]

Your definition of the ODEs is unconventional. I've always used to define coupled ODEs such that the dependent variables are in one array in the input, not as two separate ones. So, according to my understanding you should modify the zero_dmodelcc function like this:

function dy=zero_dmodelcc(C,A,y1y2,t,v_cham,m_dot_pr,m_ox)
y1 = y1y2(1); % or perhaps y1 = y1y2(1:end/2);
y2 = y1y2(2); % and if so  y2 = y1y2(end/2+1:end);
v_cham=v_cham(:);
m_ox=m_ox(:);
C=C(:);
A=A(:);
dy1 =C-(y1.*A);
dy1=dy1(:);
dy2=((y1.*m_ox)./(v_cham))+y2.*(A-m_dot_pr);
dy2=dy2(:);
dy=[dy1(:);dy2(:)]; % Should be a column-vector IIRC
end

Further you somehow define the initial conditions to be of the same size as the time-variable. That doesn't make sense. Something is likely off.

[Francesco Renzulli]

thank you, I am beginner in MATLAB, and people like you are really helpfull

Answer 2

[Cris LaPierre]

The ode solver expects the first two inputs to your odefun should be t and y (you can use any variable name you want, but this is what they represent). They are not defined in the code. Any additional input parameters come after that. Have a look at this example on the ode45 documentation page.

I agree your setup is unconventional. I would add that you use t incorrectly - both as the tspan input, and the odefun t input. Here's how you can modify the code to fix those issues at least.

ts = ts=linspace(0,burn_time,Nt);
y_0=[0,0];

[t_sol,y_sol]=ode45(@(t,y) zero_dmodelcc(t,y,C,A,v_cham,m_dot_pr,m_ox),ts,y_0);

function dy=zero_dmodelcc(t,y,C,A,v_cham,m_dot_pr,m_ox)
y1 = y(1);
y2 = y(2);