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Re: guile-user Digest, Vol 193, Issue 29

From: Tk
Subject: Re: guile-user Digest, Vol 193, Issue 29
Date: Wed, 26 Dec 2018 19:51:37 +0000

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Wednesday, 26 December 2018 12:43, Zelphir Kaltstahl <address@hidden> wrote:

> On 25.12.18 18:00, address@hidden wrote:
> > > Hello Guile Users,
> > > Is there some library, that enables high performance matrix operations
> > > or even n-dimensional array operations? I am thinking of something like
> > > NumPy in the Python ecosystem. I think NumPy in turn also uses some
> > > lower level thing to do what it does. I think OpenBLAS or MKL, depending
> > > on the architecture. I wonder if there is any wrapper around OpenBLAS
> > > for Guile or something similar.
> > > I am writing a little code for matrix operations and currently I am
> > > using Guile arrays, as they are made of vectors and have constant access
> > > time, which is already great. My guess is, that this would be the right
> > > choice if using pure Guile. I am writing data abstraction procedures, so
> > > that later on I could exchange what is used to represent the data.
> > > Maybe, if there is something like NumPy or lower level, I should use
> > > that instead? (Would I have to learn how to use FFI first?)
> > > Or maybe Guile's implementation is already so fast, that it would not
> > > make that much difference to use a lower level thing?
> > > Currently I have only a little experimental program, started today, so
> > > no huge plan. OK, one can fantasize about stuff like Pandas data frames
> > > in Guile, but I have no illusion, that it is a work of a few days or
> > > even weeks. It would be nice to learn, how to use a low level thing or
> > > maybe even Pandas, if there are any such bindings for Guile. I could
> > > make the implementation use different representations, depending on a
> > > parameter or something like that.
> > > Regards,
> > > Zelphir
> > > I took a different route. Instead of merely binding functionality in a 
> > > lower level language, I use Guile to generate lean-and-mean modern 
> > > Fortran code. The building blocks can be found here: 
> > > (wanted to save this for potluck, 
> > > but here it goes ... ). Fortran compilers take care of efficient 
> > > execution on HPC platforms. Actually, it is beyond me why anyone would 
> > > bother with any other programming language when it comes to expressing 
> > > maths efficiently.
> >
> > I built a pseudo-spectral Navier-stokes solver that can work on MPI, 
> > shared-mem (OpenMP), and hopefully soon GPU/Xeon accelerators (OpenMP 4) 
> > atop of schemetran. I still need to see about publishing it under an Libre 
> > licence.
> Hi Tk,
> That looks interesting. I've only used OpenMP once in a university
> lecture, in a pretty simple way (just adding some annotations to some
> loops to parallelize them) on a normal desktop machine. I have a few
> questions about your library:
> What are the requirements in terms of installed software? (For example:
> Do I need something Fortran installed? Or is GCC handling it all?)
> What do you mean by "on HPC platforms"? Does that imply, that it would
> not produce efficient execution on desktop machines?
> Thanks for sharing your project, I will have to take a look at how to
> use it.
> Regards,
> Zelphir

Hi Zelphir,

The requirements are guile >=2.0, fortran compiler that understands bits of 
2003/2008 standards used in the "library" (which should rather be thought of as 
a set of lego pieces) and GNU Make. The oldest gfortran compiler that I know 
works for certain with schemetran is gfortran 4.8.2. As for Intel, I've only 
tested it with v17 and greater, but I'm fairly confident anything >v13 should 
work, too. In addition, I ran tests with flang 7.0.0 (from clang/AOCC suite) 
and that suprisingly worked, too (suprisingly because they claim they fully 
support only Fortran 2003).

Schemetran itself is for the moment only helping you write pure Fortran code. 
So, no OpenMP directives are currently included. This was a design decision, 
because compiler directives, even when standardised, are dirty. I have some 
plans in that direction, but this will be something separate from schemetran 
(once I pull it from the guts of my incompressible MHD code).
That being said, schemetran can be used to generate coarray fortran (part of 
2008 and later standard extensions) which current fortran compilers usually 
implement on top of MPI parallelism (at least, that used to be the case when I 
last looked into this).

Some fortran compilers (say, Intel Fortran) can auto-parallelise your code even 
if coarray extensions are not used. This is almost always done using threads.

Even if a compiler doesn't generate parallel code, it should be able to 
efficiently optimise array operations so that all vector based capabilities of 
present day processors are properly exploited (SSE, AVX). Some care needs to be 
taken when writing code that compilers can recognise as SIMD vectorisable and 
schemetran helps you with that (chiefly by not overcomplicating things much).

I realise I deviated from your questions a bit, so let me get back on track. 
Yes, all of the things mentioned can run on a normal CPU. Vector instructions 
such as SIMD can be used anywhere, OpenMP on any multicore CPU (so, 
realistically anywhere these days), even MPI which was designed for distributed 
computing can be used on a single CPU (since mainstream MPI distributions try 
hard to turn your message passing into shared memory accesses behind your back).

Hope this helps,


PS Nothing prevents you of adding OpenMP statements by hand into the mix by 
modifying some of the schemetran directives.

PPS I hope nobody on Guile mailing list is going to shoot me for advertising 
Fortran as a scientific language of choice ;-P .

PPPS For those guys who want ndarray functionality in Guile .. do you actually 
intend to write complicated algebraic expressions using LISP-like notation? 
That's brave. I hope no nuclear facility melts down as a consequence of someone 
messing up transcription of normal math into brackets :) .

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