debugging problem with ode45

I'm a matlab beginner,now have problems with the following code function dy=co2(t,y); %t=[0:1:3000]; y=ones(12,1); dy=ones(12,1); % a column vector dy(1)=0.076*1e-16*y(2)+341.28*y(6)-682.56*y(1)+341.28*y(11)-0.4439*1e-9*y(1)*y(1)/(5.42*1e7+1800*y(2)+30133*y(1))/(y(1)+15+0.0313*y(3)); dy(2)=-0.413681e3*y(2)-0.0716*1e-16*y(2)+0.2068*1e3*y(4)+0.2068*1e3*y(5); dy(3)=1.86*1e-9*y(1)*y(1)/(5.42*1e7+1800*y(2)+30133*y(1))/(y(1)+15+0.0313*y(3))-159.1*(y(3)-250); dy(4)=0.02471e-15*y(7)/(y(7)+130)-0.0856*1e3*(y(4)-y(2)); dy(5)=0.02471e-15*y(8)/(y(8)+130)-0.0856*1e3*(y(5)-y(2)); dy(6)=39*(y(1)-y(6))+0.2445*1e-11*y(7)/(5.42*1e7+1800*y(7)+30133*y(6))-0.0508*1e-9*y(6)/(5.42*1e7+1800*y(7)+30133*y(6))-1.4286*1e-3*(y(6)-y(9)); dy(7)=0.0055*1e-15*y(10)/(y(10)+130)+0.0508*1e-9*y(6)/(5.42*1e7+1800*y(7)+30133*y(6))-0.2445*1e-11*y(7)/(5.42*1e7+1800*y(7)+30133*y(6))-6.8*1e-18*y(7)/(y(7)+130); dy(8)=3.96*1e-15*y(12)/(y(12)+130)-3.96*1e-15*y(8)/(y(8)+130); dy(9)=33.5641*1e-3*(y(6)-y(9))+1.034*1e-10*y(10)/(5.42*1e7+1800*y(10)+30133*y(9))-2.148*1e-9*y(9)/(5.42*1e7+1800*y(10)+30133*y(9))-14.76*1e3*(y(9)-1); dy(10)=9.031*1e3*(13.5-y(10))+2.15*1e-9*y(9)/(5.42*1e7+1800*y(10)+30133*y(9))-1.034*1e-10*y(10)/(5.42*1e7+1800*y(10)+30133*y(9))-0.128*1e-15*y(10)/(y(10)+130); dy(11)=0.2268*1e-3*(y(1)-y(11))+1.034*1e-10*y(12)/(5.42*1e7+1800*y(12)+30133*y(11))-2.149*1e-9*y(11)/(5.42*1e7+1800*y(12)+30133*y(11))-10.25*1e3*(y(11)-1); dy(12)=9.0308*1e3*(13.5-y(12)+2.149*1e-9*y(11)/(5.42*1e7+1800*y(12)+30133*y(11))-1.0343*1e-10*y(12)/(5.42*1e7+1800*y(12)+30133*y(11))-0.1282*1e-15*y(12)/(y(12)+130)); %In this example we change the error tolerances using the odeset command and solve on a time interval [0 12] with an initial condition vector zeros(12,1) at time 0. options = odeset('RelTol',1e-4,'AbsTol',[1e-4 1e-4 1e-5]); [t,y]=ode45(dy,[0 3000],ones(12,1),options)

the running result is: ??? Error using ==> exist The first input to exist is a string. Error in ==> odearguments at 80 if (exist(ode)==2) % M-file Error in ==> ode45 at 173 [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ... Error in ==> co2 at 20 [t,y]=ode45(dy,[0 3000],ones(12,1),options)