solving differential equation system with ode45

I have a system of second order diferential equations:

I would like to solve this system using ode45.

here is what i tried for solving the system:

function dYdt = odefcn(t,Y)
load STIFF_VALUES
load THETA

A=6.58e5;B=1.8;C_1=0.3083e-3;C_2=0.4439e-3;D=6.58e5;E=1.8;F=60e3;									
G=51.6831;H=0.96e-1;I=F*30/25;J=70.4769;K=2e-1;M=67e-3;
L = interp1(THETA,STIFF_VALUES,t);									
								
N=L*((Y(1)-Y(3))-(G*Y(5)-J*Y(7)))+M*((Y(2)-Y(4))-...
	(G*Y(6)-J*Y(8)));
dYdt = [ Y(2);
    1/C_1*(A*Y(1)+ B*Y(2)-N);
    Y(4);
    1/C_2*(-D*Y(3)- E*Y(4)+N);
    Y(6);
    1/H*(F+G*N);
    Y(8);
    1/K*(-I-J*N)];
		 
end

init_cond = [0,0,0,0,0,2400,0,2000]';
t_interval=[0 10];
[t,y]=ode45(@(t,Y) odefcn(t,Y) , t_interval , init_cond);

I got NaN values for y(:,1).

*I tried "ode15s" which returns the following warning!

Warning: Failure at t=1.451171e-02. Unable to meet integration tolerances without reducing the

step size below the smallest value allowed (2.775558e-17) at time t.

[Torsten]

The setup of the system for ODE45 looks correct.

So it remains to check the initial conditions and the model parameters.

You should load THETA and STIFF_VALUES in the program where you call ode45 and pass the arrays to the solver as

[t,y]=ode45(@(t,Y) odefcn(t,Y,THETA,STIFF_VALUES) , t_interval , init_cond);
...
function dYdt = odefcn(t,Y,THETA,STIFF_VALUES)
...
end

This saves time.

Further, take care that THETA(1) <= t <= THETA(end). Otherwise, interp1 will return NaN for L.