[SciPy-dev] petsc - UMFPACK and scipy

[David Cournapeau]

Nils Wagner wrote:
> Ondrej,
>
> Please can you show me an example where petsc solvers are "better" than
> UMFPACK.
>
> Nils
>
> 4) About the petsc - I know it's another dependence. However, I
> noticed you are using umfpack in SciPy. So why not petsc? I think it
> contains much more (sometimes better) solvers (depends on the
> problem). It's seems logical to me, to either use nothing, or the best
> library available, which I believe is petsc.
I can give you one situation where adding dependency makes things more 
complicated: when you are a packager. I am trying to "evangelize" 
numpy/scipy, and one problem people face is installation. When you are a 
user, adding dependency is great, it gives you more code, more API to 
leverage. When you are a packager, each dependency is a mess.

I am working on rpm and debian package of numpy and scipy, and 99.9 % of 
the problems are the dependencies. LAPACK and BLAS are already quite 
difficult to package correctly (debian was the only distribution to do 
it correctly for a long time), UMFPACK is kind of a pain to compile too 
(depends on two other packages), and let's not even start talking about 
ATLAS, which pose significant challenges by its very nature (again, only 
debian has done it correctly, Fedora copying their method). And I have 
only experience on linux, where at least every distribution uses the 
same compiler suite.

Most of those libraries are not really commonly used, and as such, are 
not provided by distributors most of the time.

I wouldn't be surprised if this is one of the reason why Robert is 
reluctant to add more dependencies.

David