Taking derivatives of an array variable

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Author Message   Igor Bolotnov (boloti) New member Username: boloti Post Number: 2 Registered: 12-2007 Posted on Tuesday, March 11, 2008 - 11:37 am:    Hello! I'm writing a code with 8 similar equations. (FlexPDE 5.0.19 1D Professional). Since it is impossible to define array variables, I do it this way: variables u(threshold=2.0) k1(threshold=2.0) k2(threshold=2.0) k3(threshold=2.0) k4(threshold=2.0) k5(threshold=2.0) k6(threshold=2.0) k7(threshold=2.0) k8(threshold=2.0) definitions K = array(k1, k2, k3, k4, k5, k6, k7, k8) TK = k1+k2+k3+k4+k5+k6+k7+k8 Then, I have a problem: dx(TK) or dx(k1) results in a proper derivative while an attempt to apply dx(K[1]) results in zero value. So, I'm missing some dx terms in my equations when I specify the Right Hand Side of the equations as: ! Diffusion term D(j) = dx(nu_cl*dx(K[j])) ! This one does not work! ! Turbulent Diffusion term ARG0(j) = nu_T(j)*dx(TK) ! This one works! TURD(j) = dx(ARG0(j)) RHS(j) = P(j) - eps(j) - epsY(j) + TR(j) + D(j) + TURD(j) equations u: lambda*rho*dt(u) = div(rho*(nu_cl+TNu_T)*grad(u)) - dPdx k1: lambda*dt(k1) = RHS(1) k2: lambda*dt(k2) = RHS(2) k3: lambda*dt(k3) = RHS(3) k4: lambda*dt(k4) = RHS(4) k5: lambda*dt(k5) = RHS(5) k6: lambda*dt(k6) = RHS(6) k7: lambda*dt(k7) = RHS(7) k8: lambda*dt(k8) = RHS(8) Do you know how to get the derivative values from arrays defined above? (without tediously specifying each equation separately which may result in a bunch of typos) I have removed all irrelevant (IMHO) information, please let me know if I missed to provide anything. Thanks a lot!   Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 1080 Registered: 06-2003 Posted on Tuesday, March 11, 2008 - 01:15 pm:    ARRAYS in FlexPDE version 5 are quite restricted. The facility was added primarily to allow compacting of expressions in domain definition. ARRAY components must be parse-time constants. FlexPDE cannot handle arrays of variables. Your constructs like RHS(j) are really parameterized definitions, and as such are expanded as function calls. But this won't work to access an indexed array of variables. You'll have to simply use copy and paste to replicate copies and manually patch in the variable number. Sorry.