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Topic: Boundary conditions in PDE solver ?
Replies: 1   Last Post: Mar 15, 2013 3:55 AM

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Torsten

Posts: 1,472
Registered: 11/8/10
Re: Boundary conditions in PDE solver ?
Posted: Mar 15, 2013 3:55 AM
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D R G <grimesd2@gmail.com> wrote in message <5eb70b4f-9f30-460e-87c0-b12526e7ad47@googlegroups.com>...
> I'm having some difficulty understanding the required input for matlab PDE boundary conditions. Essentially, I have a function U that has the following boundary conditions;
>
> U(r) = 0
> dU/dr(r) = 0
>
> how can I code these up into the form
>
> pl =
> ql =
> pr =
> qr =
>
> I understand they must be the the p(x,t...) + q(x,t...).. = 0 form, but I am not sure how to proceed..


Put your boundary conditions in the required form:
u=0 can be written as u+0*f = 0, thus p=u and q=0 ;
du/dr=0 can be written as 0+1*f=0, thus p=0 and q=1
(assuming that f=constant*du/dx for your system of pdes).
Thus
pl=0, ql=1, pr=ur, qr=0
(if u=0 is the boundary condition at the right end of your domain and du/dr=0 is the boundary condition at the left end of the domain).

Best wishes
Torsten.



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