Help: Finds difficult in solving this coupled ordinary differential equations using ODE45 ??

I have been solving these coupled ordinary differential equations using ODE45

Function file (first file)

function dy=pair1(t,y)

dy=zeros(3,1);

dy(1)=(a/(1-y(3)).^b*sigma*(1-y(2))*coth(b*sigma*(1-y(2)))*sinh(b*sigma*(1-y(2))));

dy(2)=(hstress/sigma)*(1-(y(2)/hstar))*((a/(1-y(3)).^b*sigma*(1-y(2))*coth(b*sigma*(1-y(2)))*sinh((b*sigma*(1-y(2))))));

dy(3)=d*(a/(1-y(3)).^b*sigma*(1-y(2))*coth(b*sigma*(1-y(2))))*sinh(b*sigma*(1-y(2)));

end

Second file

a=0.2044e-6;

b=0.1855e-1;

d=1;

hstress=0.4285e05;

hstar=0.5113;

T=503;

sigma=180;

tspan=0:0.01:70;

initial_conditions=[0;0;0]; %change the intial condition according to your values

[t,y]=ode45(@(t,y)pair1(t,y),tspan,initial_conditions) %function call

plot(t,y)

Ended up in the following error:

Undefined function or variable 'a'.

Error in pair1 (line 3)

dy(1)=(a/(1-y(3)).^b*sigma*(1-y(2))*coth(b*sigma*(1-y(2)))*sinh(b*sigma*(1-y(2))));

Error in @(t,y)pair1(t,y)

Error in odearguments (line 87)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 113)

[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in Untitled6 (line 11)

[t,y]=ode45(@(t,y)pair1(t,y),tspan,initial_conditions) %function call

Please anyone help me to sort out this problem..

Answer 1

[Torsten]

Put the constants (a,b,d,..) in your first file.

[madhan ravi]

% changes to be made
function dy=pair1(t,y,a,b,d,hstress,hstar,T)
[t,y]=ode45(@(t,y)pair1(t,y,a,b,d,hstress,hstar,T),tspan,initial_conditions)