ode45 coupled first degree ODEs

I want to solve two coupled ODEs in matlab using ODE45, but get an error that says U"nable to perform assignment because the left and right sides have a different number of elements". I dont know really what the problem is here and have tried severad changes but did not fix it.

Code:

function dz = myode(v,z)

a = 0.4;

b = 0.001;

c = 0.001;

d = 0.9;

dz = zeros(2,1);

dz(1) = a*z(1)-b*z(2)*z(1);

dz(2) = c*z(1)*z(2)-diff(z(2));

end

I call it as:

[v z] = ode45(@myode,[0 40],[2 6])

Hope someone can help

[esat gulhan]

What is your differantial code. can you give your diff equation dz/dv....

Answer 1

[Alan Stevens]

Do you mean something like this:

[v, z] = ode45(@myode,[0 40],[2 6]);

plot(v,z)
function dz = myode(~,z)
a = 0.4;
b = 0.001;
c = 0.001;
d = 0.9;  
dz = [a*z(1)-b*z(2)*z(1);
      c*z(1)*z(2)-d*z(2)];
end

You had diff(z(2)), but d was unused, so I assumed you meant d*z(2). However, this might not have been what you wanted!

[Serhat Unal]

oh thank you I have just read it wrong and thought it was an derivative. Therefore It became very confusing but now it works, thanks!