Trouble with system of ODEs: dsolve

Hello,

Sorry if this is an obvious answer, but I am fairly new to Matlab and want to make sure I'm doing this correctly.

I am trying to model a biological system through a system of 5 ODEs. My code is below with the constant values k1-k5 currently with values of 1, but will be filled in with actual values using experimental data. I am getting an error stating:

"Warning: Explicit solution could not be found. > In dsolve (line 201) "

My question is, am I setting this code incorrectly or is it just that my constants are such that it is not allowing the equations to converge? Basically, once I get the actual k values will it work or is there something fundementally wrong with the way I set it up?

    if true
      % % Symbolic Variables
  syms P(t) Cx(t) Ci(t) Co(t) Cdna(t) k1 k2 k3 k41 k42 k5 mu Y

% Constants Definitions

k1  == 1;     % Product rate constant;
k2  == 1;     % Nonproducing -> Producing rate constant
k3  == 1;     % Death rate constant of producing cells
k41 == 1;     % DNA transfection, 1/cells*min
k42 == 1;     % DNA transfection, 1/mg*min
k5  == 1;     % DNA precipitation/aggragation
mu  == 1;     % Cell growth rate constant, 1/min

%ODE Definitions

eqn1 = diff(P)    == k1*P;
eqn2 = diff(Cx)   == k2*Ci - k3*Cx;
eqn3 = diff(Ci)   == k41*Co*Cdna - k2*Ci;
eqn4 = diff(Co)   == mu*Co - k41*Co*Cdna;
eqn5 = diff(Cdna) == -k42*Co*Cdna - k5*Cdna;

% Initial Conditions
c1 = P(0)    == 0;
c2 = Cx(0)   == 0; 
c3 = Ci(0)   == 0;
c4 = Co(0)   == 20E6; %cells/ml
c5 = Cdna(0) == 20; %mg/ml of DNA from James

   [PSol(t) CxSol(t) CiSol(t) CoSol(t) CdnaSol(t)] = dsolve(eqn1, eqn2, eqn3, eqn4, eqn5, c1, c2, c3, c4, c5);
    end

[Torsten]

Use ode15s (i.e. a numerical solver) instead of a symbolic one.

Your system appears too difficult for an analytical solution.

Best wishes

Torsten.