@umi 

Sorry yi (i=1..7), y is concentration ( i used C sometimes)..

@umi 

Sorry yi (i=1..7), y is concentration ( i used C sometimes)..

@hirnyk 

i=1..7

@hirnyk 

i=1..7

Thanks for your feedback

I have tried to solve a simple 9 ODEs with 9 unknown functions and works well, however when I increase the complexity by adding diff(Ci(x),x,x) and diff (phi[s](x),x,x) in the ODEs, problem occured. It keeps giving me error of unable to convert to explicit first order. So I don't think no 2. is a problem.

However when I use the ODE advisor for phi[s](x) it says_2nd_order_missing_y. Do I have to do any changes with that.

Please help

Thanks for your feedback

I have tried to solve a simple 9 ODEs with 9 unknown functions and works well, however when I increase the complexity by adding diff(Ci(x),x,x) and diff (phi[s](x),x,x) in the ODEs, problem occured. It keeps giving me error of unable to convert to explicit first order. So I don't think no 2. is a problem.

However when I use the ODE advisor for phi[s](x) it says_2nd_order_missing_y. Do I have to do any changes with that.

Please help