Question: System of ODE with ICs

Hi,

I have the following set of ODE:

sys := diff(U(t), t) = Itot/C-U(t)/(R*C), diff(U(t), t) = (Itot-I1(t))/C, diff(U(t), t) = I2(t)/C

The general solution is easily obtained by:

sol1 := dsolve({sys})

SOLUTION: sol1:={U(t)=Itot R+(e)^((-(t)/(R C))) _C1,I2(t)=-((e)^((-(t)/(R C))) _C1)/(R),I1(t)=(Itot R+(e)^((-(t)/(R C))) _C1)/(R)}

However, I cannot get the solution for initial conditions. In fact, we only need one initial condition, to solve for _C1:

IC:=U(0)=0  #Alternatively: I1(0)=0 or I2(0)=Itot.

If I try with:

sol2 := dsolve({sys,IC})

no solution is displayed, no matter which or how many of the above ICs I use.

If I try with:

sol3 := combine(dsolve({sys} union {ics}))

I get: Error, (in combine) combine uses a 1st argument, F, which is missing

Question: How do I get the solution which includes ICs? ( _C1 is expected to be -Itot*R)

Thanks in advance.