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Mass balance issue when solving an elliptic diffusion problem using pde toolbox

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Mohammad Monfared
Mohammad Monfared 2014-1-21
编辑： Mohammad Monfared 2014-1-30
Hi
I'm trying to solve a diffusion like, elliptic equation using pde toolbox. I used 'pednonlin' function but the answer I get, gets me a bit confused regarding mass conservation issue since the solution should be steady-state.
Here are more about problem:
The equation is simply -div(K(u)*del(u)) = 0 on a rectangular domain with Dirichlet B.C. on top and bottom and no flux B.C. on side boundaries. But when I plot the solution using:
[cux,cuz] = pdecgrad(p,t,c,u) ;
pdeplot(p,e,t,'flowdata',[-cux;-cuz])
the flux has a pattern which induces mass is not conserved!
Does anyone have an idea where I'm going wrong?
Thanks a lot.

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Mohammad Monfared
Mohammad Monfared 2014-1-30
编辑：Mohammad Monfared 2014-1-30
The issue was that the Jacobian has to be calculated using 'full' parameter, not 'fixed' or 'lump'.

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