Solving Differential equations in Matlab, ode45

Question

I'm trying to solve a system with three differential equations with the function ode45 in Matlab. I do not really understand the errors i am getting and i could use some help understanding what im doing wrong.

The differential equations are the following:

F1 = -k1y1+k2(y2-y1)
F2 = -k2(y2-y1)+k3(y3-y2)
F3 = -k3(y3-y2)

And my code in Matlab is this:

function dz = kopplad(t, z)
global m1 m2 m3 k1 k2 k3 
dz = [z(2)
-k1*z(1)/m1 + k2*(z(2)-z(1))/m1
z(4)
-k2*(z(2)-z(1))+k3(z(3)-z(2))/m2
z(6)
-k3(z(3)-z(2))/m3];

global m1 m2 m3 k1 k2 k3
m1 = 0.75; m2 = 0.40; m3 = 0.65;
k1 = 0.85; k2 = 1.1; k3 = 2.7;
[t, z] = ode45(@kopplad, [0, 50], [0 -1 0 1 0 0]);
plot(t, z(:,1)) 
hold on
plot(t,z(:,3),'--')
plot(t,z(:,5),'*') 
legend('y_1', 'y_2', 'y_3');
hold off

The errors I'm recieving are the following:

Attempted to access k3(1.00002) ; index must be a positive integer or logical.

Error in kopplad (line 3) dz = [z(2)

Error in ode45 (line 262) f(:,2) = feval(odeFcn,t+hA(1),y+f*hB(:,1),odeArgs{:});

Error in diffekv (line 6) [t, z] = ode45(@kopplad, [0, 50], [0 -1 0 1 0 0]);

Answer 1

A while passed since I did some Matlab programming, but as far as I remember, you should pass variables to the function, ie write @(x,y)kopplad(x,y) , if I understand you code in a correct way. If the rest (global variables and equations) are correct, everything shall be fine.