Question: error in pdsolve

I am solving a PDE coupled with an ODE, as following:

pde1:=diff(RR(tau), tau) = dRdt                                                                               (1)

where: dRdt := t0*Dif1*(csh(RR(tau), tau)-Csout(1, i-1))/(12*Pi*RR(tau)*rho)

--> after substituting the constants, eq. (2) is obtained:

diff(RR(tau), tau) = 7.543466567*10^(-17)*csh(RR(tau), tau)/(Pi*RR(tau))    (2)

pde2:=(diff(csh(rh, tau), tau))/t0 = rh*dRdt/RR(tau)+(diff(Dif*rh^2*RR(tau)*(diff(csh(rh, tau), rh)), rh))/(RR(tau)^2*rh^2)                                                           (3)

(Do not matter with the constants, they are all specified)

--> after substituting the constants in (3), eq. (4) is obtained:

1690.558181*(diff(csh(rh, tau), tau)) = Typesetting[delayDotProduct](7.543466567*10^(-17), rh, true)*csh(RR(tau), tau)/(RR(tau)^2*Pi)+(Typesetting[delayDotProduct](5.306406642*10^(-9), rh, true)*RR(tau)*(diff(csh(rh, tau), rh))+2.653203321*10^(-9)*rh^2*RR(tau)*(diff(csh(rh, tau), rh, rh)))/(RR(tau)^2*rh^2)                                                                                                (4)

Boundary and Initial Conditions:

{RR(0.) = 8.35177808555860112*10^(-8), csh(rh, 0) = .983525883709509663, (D[1](csh))(0, tau) = 0, (D[1](csh))(1, tau) = 3.022000000*10^(-10)*csh(RR(tau), tau)/(Pi*RR(tau)^2)}

When I try to solve using:

pds:= pdsolve([pde1, pde2], IBC, numeric), or

pds:= pdsolve([pde1, pde2], IBC, numeric, time = tau, range = 0 .. 1, timestep = 1/20)

maple returns the following error:

Error, (in pdsolve/numeric/process_PDEs) variable(s) {rh} are in the PDE system but are not dependent or independent variables

Anybody knows what is happening?

Thank you a lot.



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