ode45 function error: function must return a coloumn vector. how can i run this?

plz help me.my editor is same as this:

function xdot = vanvusse(t,x) % % (c) b.w. bequette % 25 july 94 % revised 20 july 96 % % dynamic model for the van de vusse reaction % % to use this function file with ode45: % % [t,x] = ode45('vanvusse',t0,tf,x0) % % where t0 is the initial time (usually 0) % tf is the final time % x0 is the initial condition for the states % % x = states % x(1) = concentration of A % x(2) = concentration of B % t = time % % fov = dilution rate % ca = concentration of a % cb = concentration of b % caf = feed concentration of a % % the reaction scheme is % % A --> B --> C % (k1) (k2) % 2A --> D % (k3) % k1 = 5/6; % rate constant for A --> B (min^-1) k2 = 5/3; % rate constant for B --> C (min^-1) k3 = 1/6; % rate constant for A + A --> D (mol/(liter min)) caf = 10; % feed concentration of A, mol/liter % % for step changes in fov, use the following % fov = 4/7 + delf; % % use familiar notation for the states % ca = 2; cb = 1.117; fov = 4/7; % % modeling equations % dcadt = fov*(caf - ca) -k1*ca - k3*ca*ca; dcbdt = -fov*cb + k1*ca - k2*cb;

% % derivatives placed in vector notation % xdot(1) = dcadt; xdot(2) = dcbdt; % end of file

then i wrote at command window this:

[t,x]=ode45('vanvusse',[0,5],[0 0]);

and I see that warning on matlab.

??? Error using ==> odearguments at 113 VANVUSSE must return a column vector.

Error in ==> ode45 at 173 [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

I wanna plot(t,x) but ode is not working. how do i run this ?

Answer 1

[Mischa Kim]

Tugce, either add

 xdot = zeros(2,1);

right before you start assigning values to the two xdot components, or, rewrite the two scalar equations for xdot(1) and xdot(2) as a vector equation:

 xdot = [dcadt;...
         dcbdt];

[Mischa Kim]

If I run the code I do get non-constant output. In fact you get linearly increasing function values, which is to be expected because the derivatives ( dcadt, dcbdt ) are constants.

 function test()
 [t,X] = ode45(@vanvusse,[0,5],[0 0]);
 plot(t,X(:,1),t,X(:,2))
 end

 function xdot = vanvusse(t,x)  
 k1    = 5/6;  k2 = 5/3;  
 k3    = 1/6;  caf = 10;  
 fov   = 4/7 + 0;          % delf not defined, set to zero
 ca    = 2;    cb = 1.117; 
 fov   = 4/7;  
 dcadt =  fov*(caf - ca) - k1*ca - k3*ca*ca; 
 dcbdt = -fov*cb + k1*ca - k2*cb;
 xdot  = [dcadt; ...
          dcbdt];
 end

Copy-paste the above code into one m-file, name it test.m and run it.

Also, please post follow-up questions and comments as comments , not answers.

Answer 2

[tugce]

thank you so much it is running now. now ı have a lot of data at my command window as expecting but all data are same, where is the problem??