Re: 1D PDE solver for Octave

[Bill Greene]

>sure, were is the code?
OK, great.

The source code is here:

https://github.com/wgreene310/pde1d

Unfortunately, my approach to building this is somewhat ad-hoc

at this point so you might find that challenging. I can send you a

Linux Makefile if you are sufficiently motivated.

Alternatively, I have a pre-built Linux binary here:

https://drive.google.com/folderview?id=0B0HVh_MUHujMU0MzY2FxSlVUWWs&usp=sharing

that seems to work fine with Octave 4.02 on my system.

Let me know if you run into problems with either approach.

Thanks.

Bill

On Thu, Jun 30, 2016 at 9:54 AM, Carlo De Falco <address@hidden> wrote:

On 30 Jun 2016, at 15:08, Bill Greene <address@hidden> wrote:

> Thanks for taking the time to reply although I am disappointed
> that you didn't address any of my issues.

As I said in my previus email I needed more info in order to address
some of them.

> I am using the C API to ida; my code is written in C++.

This is the same approach Franceso is using in ode15i/ode15s.

There may be lots of code duplication, it would be nice to compare
your implementations ...

> My code is currently using a simple linear interpolation in the
> spatial dimension and then using ida to solve the resulting system
> of ODE.

So to summarize, given a parabolic PDE you discretize in space
using linear finite elements / first order finite differences
the solve the resulting ODE with BDF time-stepping via IDA,
is this correct?

> I intend to improve the spatial discretization in the future
> but the current implementation could certainly be considered "inferior"
> to pdepe. I'm not trying to duplicate pdepe-- just support the same
> problem class and the command line interface as closely as possible.

If my interpretation of your algorithm above is correct, it sounds
like, in order to reduce code duplication, this could be implemented
like a thin wrapper around BIM and ode15i or daspk, but we need to see
the code to be more specific.

> I should say one more thing about Sundials ida. The latest version of
> ida is only just "adequate" to support my current implementation,
> mainly because its sparse matrix support is rather rudimentary. I am
> hoping they will improve ida in this area and expect that for the
> foreseeable future I'll want to be using the very latest ida release.
>
> I am aware of the ongoing Octave ode15s work; I alluded to that in my original
> message.

I missed that, sorry. Replying below.

>> I know that some work is ongoing using Sundials ida to improve the
>> Octave ODE solvers. But I'm unclear on when or if this might result
>> in the Sundials libraries being available in Octave.

The changes for linking Octave to Sundials in Francesco's code are essentially
done, but I'm not sure whether they'll be merged into core for the 4.2 or 4.4
release ...

If you want to start using those you can just clone Francesco's repo
from bitbucket and build Octave from there.

>
> I would be happy for anyone to try the current code. At this point, I
> consider it to be solid beta-quality code.

sure, were is the code?

>
> Thanks.
>
> Bill


c.