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[Johan Hake <question139887@xxxxxxxxxxxxxxxxxxxxx>]

Question #139887 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/139887

Johan Hake proposed the following answer:
On Sunday January 2 2011 02:25:13 Sungick Kim wrote:
> Question #139887 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/139887
> 
>     Status: Answered => Open
> 
> Sungick Kim is still having a problem:
> Initially, I wanted to change the actual boundary domain.
> After checking your answer out,
> I think that changing the value of Dirichlet boundary condition for a fixed
> boundary would be correct. So I tried this code below. However, the value
> is not changing.
> Could you give me a hand again?
> 
> ---------------------------------------------------------------------------
> ----------------- boundary = compile_subdomains("on_boundary")
> 
> # approximated step function whose value is 1 for x[0] < t
> g = Expression("0.0 + 1.0/(1+exp(10*(x[0]-t)))")
> 
> BC = DirichletBC(Q1, g1, boundary)
> 
> # Parameters for time stepping
> T = 10.0
> dt = 0.1
> t = 0.0
> 
> while t < T:
> 
>     t += dt
>     # solve problem
> ---------------------------------------------------------------------------
> -----------------

You need to update t in your expression:

...

  while t < T:

      t += dt
      g.t = t #!!!
      # solve problem


Johan

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