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Re: [ff3d-users] Code to solve Fick's law, what's wrong??!!

 From: Arun Viswanathan Subject: Re: [ff3d-users] Code to solve Fick's law, what's wrong??!! Date: Sat, 15 May 2004 08:24:31 -0700 (PDT)

```Hey Stephane,

I am so sorry to be bothering you so often, the whole
thing is new to me, that's why I have too many
doubts....here's yet another...:)...

In the example of the Euler's equation that you sent
me, 'dt' is simply declared as any other variable. In
my equation of Fick's law, I don't think I can do
that. The equation I am trying to solve goes this way:

d/dt [C(x,t)] = D * d^2/dx [C(x,t)]
where 'd/dt' is a partial derivative with respect to
't' and 'd^2/dx' is a second order partial derivative
with respect to 'x'.

I have coded this as 'dt(C) = D*div(grad(C))', but
'div(grad)' is in terms of 'x'. My doubt is how to
express it in terms of 'x' when the other term is
expressed in 't'?? I really appreciate your patience
with me and my queries.

Thanks so much. Best regards,
Arun.

--- Stephane Del Pino <address@hidden> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
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>
> > solve(C) in M
> > {
> >         pde(C)
> >            dt(C) = D * div(grad(C));
> > };
> You have to write the time discretization scheme by
> yourself.
> Here comes an implicit Euler scheme.
>
> function C0 = x*y*z;
> double dt = 0.1; // time step
> int i;
> for (i=0; i<5; ++i) {
>   solve (C) in M
>   {
>     pde(u)
>       C - div(dt*grad(C)) = C0;
>   }
>   C0 = C;
> }
>
> Best regards, Stephane.
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