must be that i need to upgrade to version 13 so?

Thanks for all the help guys, i've tried your suggestions on a simpler case where there are only 3 functions, not 4. It works just fine. Problem that I'm seeing now is that the 4 function case (the one we've been talking about) won't stop evaluating. It seems to be stuck in a loop. I tried exactly what Jean-Marc suggested (i even copied and pasted the commands) but when I execute, it is stuck evaluating, it's been 3240 seconds now. How long did it take you Jean-Marc? What could be wrong? I am using Maple 11 on Apple OSX, FYI.

Hello Thanks, but I tried something like that already. The error messages are below, maybe they can help because I am very new to Maple and don't know a lot yet. sys := diff(f1(x), x, x)-f1(x)+f2(x) = 0, diff(f2(x), x, x)-f2(x)+f3(x)+b1*(f1(x)-f2(x)) = 0, diff(f4(x), x, x)+b3*(f3(x)-f4(x)) = 0, diff(f3(x), x, x)-f3(x)+f4(x)+b2*(f2(x)-f3(x)) = 0; ics := f1(0) = 0, f2(0) = 0, f3(0) = 0, f4(0) = (r1+r2+r3+r4)/r4; sol := dsolve([sys, ics]); Error, (in dsolve/IC) invalid arguments; expected an equation, or a set or list of them, received: {{diff(diff(f2(x), x), x)-(159543/100000)*f2(x)+f3(x)+(59543/100000)*f1(x) = 0, diff(diff(f3(x), x), x)+(353163/500000)*f2(x)-(353163/500000)*f3(x) = 0, diff(diff(f1(x), x), x)-f1(x)+f2(x) = 0}} dsolve([sys]) Error, (in ODEtools/odsolve) invalid input: `PDEtools/sdsolve` expects its 1st argument, SYS, to be of type {set({algebraic, `=`, `<>`}), list({algebraic, `=`, `<>`})}, but received [{diff(diff(f2(x), x), x)-(159543/100000)*f2(x)+f3(x)+(59543/100000)*f1(x) = 0, diff(diff(f3(x), x), x)+(353163/500000)*f2(x)-(353163/500000)*f3(x) = 0, diff(diff(f1(x), x), x)-f1(x)+f2(x) = 0}]

That worked a charm, thanks a million