MATLAB: ODE45 – seperate function from commandfile

MATLABode45urgent

I'm calculating some chemical reactions using the code below but I would like to bring out the "incode" function concentration to a seperate functionfile. I've made a try in the code at the bottom.
s = 1;
q = 1; 
w = 0.1610;
% define y = [α(t) β(t) γ(t)] = [y(1) y(2) y(3)], then
concentration = @(t,y) [...
    s * (y(2) - y(1)*(y(2)+1) - q*y(1)^2)   % α'(t)

    (-y(2) - y(1)*y(2) + y(3))/s            % β'(t)

    w * (y(1)-y(3))                         % γ'(t)

];
% initial value
y0 = [30 1 30];
% time span 
t_span = [0 10];
% solve numerically
[t, y] = ode45(concentration, t_span, y0);
plot(t,y);
Function draft
function concentration = func(t,y) 
concentration=[
    s * (y(2) - y(1)*(y(2)+1) - q*y(1)^2)   % α'(t)
    (-y(2) - y(1)*y(2) + y(3))/s            % β'(t)
    w * (y(1)-y(3))                         % γ'(t)
];
I'm a bit lost and would appreciate some help to do this.

Best Answer

Save this as file:
function c = func(t, y, s, q, w) 
c = [s * (y(2) - y(1)*(y(2)+1) - q*y(1)^2); ...   % α'(t)
     (-y(2) - y(1)*y(2) + y(3))/s; ...            % β'(t)
     w * (y(1)-y(3))];                            % γ'(t)
Then start the integrator like this:
s = 1;
q = 1; 
w = 0.1610;
y0 = [30 1 30];
t_span = [0 10];
[t, y] = ode45(@(t,x) func(t, x, s, q, w), t_span, y0);
See: http://www.mathworks.de/matlabcentral/answers/1971
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