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## Re: gsl: discrete Hankel transform

 From: c. Subject: Re: gsl: discrete Hankel transform Date: Fri, 4 Oct 2013 13:51:55 +0200

```On 4 Oct 2013, at 13:48, c. <address@hidden> wrote:

>
> On 4 Oct 2013, at 12:59, Francis Poulin <address@hidden> wrote:
>
>> Hello,
>>
>> I am trying to solve Poisson's equation on a circular disk and thought I
>> might try the Discrete Hankel Transform that is part of gsl. I have gotten
>> as far as loading the package.  I found some documentation for gsl that
>> gives some information but these commands don't they don't seem to be in
>> octave (after I pkg load gsl-oct364).
>>
>> http://www.gnu.org/software/gsl/manual/html_node/Discrete-Hankel-Transform-Functions.html#Discrete-Hankel-Transform-Functions
>>
>> Does anyone have any example files I could use to learn about how to do this
>> in octave?
>>
>> Cheers, Francis
>
>
> If you don't need to stick to exactly that method for solving Poisson's
> equation,
> here is a simple example of how to solve it with the bim package [1]:
>
>>> msh = msh2m_gmsh ("circle", "clscale", ".1");
>>> msh = bim2c_mesh_properties (msh);
>>> A = bim2a_laplacian (msh, 1, 1);
>>> b = bim2a_rhs (msh, 1, 1);
>>> dnodes = bim2c_unknowns_on_side (msh, [1 2]);
>>> inodes = setdiff (1:columns(msh.p), dnodes);
>>> u = zeros (columns (msh.p), 1);
>>> u(inodes) = A(inodes, inodes) \ (b(inodes) - A(inodes, dnodes) * u(dnodes));
>>> close all
>>> graphics_toolkit fltk
>>> pdesurf (msh.p, msh.t, u)
>
> you might also want to take a look at the new fem-fenics package [2,3].
>
> c.
>
> [1] http://wiki.octave.org/Bim_package
> [2] http://wiki.octave.org/Fem-fenics
> [3] http://wiki.octave.org/Fem-fenics#Poisson_Equation

BTW, I forgot to attach the file "circle.geo" which is used in the example
above.
c.

```

circle.geo
Description: Binary data