Re: Matrix Multiplication

On 2008-01-04 15:20:18 -0400, Evgenii Rudnyi <usenet@xxxxxxxxx> said:

Hello Gordon,

Thank you for your comments.

If one were looking at this like a referee one would be questioning an
author who seems to like to use a 30 year old version of Fortran.
There are three revisions since 1977. Fortran 90 introduced a lot
of matrix operations which are never mentioned.

I have written that I know Fortran 77 only and I have mentioned that
the newer versions are available. If you are interested why, the
answer is simple - I have switched to C++ long ago.

You can find my comments Fortran vs. C++ here

http://evgenii.rudnyi.ru/doc/misc/fortran.txt

I see that you have Van Synder's citation of the Les Hatton work on
empirical error rates in real programs. C++ does not look good there.
Fortran 90 helps find some of the call mismatchs that are possible in
Fortran 77 if one uses the newer facilities. The subscript errors
would remain and are a more serious issue.

Fortran 90 has matrix multiply in the language. Why do you then
talk about implementing matrix multiply? Because you choose
to make comparisons against the 1977 standard? Perhaps you should
also use the C++ version from 30 years ago. If you can not then
perhaps that indicates that things do change.

but we do have to agree on this. Taste differs.

When an author goes out of the way to "think old" one wonders how much
of the rest of the material has the same attributes.

I would appreciate if you will be more specific here.

Both a good implementation of an interpreter and of Fortran 90 are free
to use the best available subroutine libraries for their purposes. The
GNU successor to G77 may or may not have reached the maturity of using
a highly optimized run time for matrix multiply.

Is Intel Fortran good? If you want it to, I will compile the code with
it the next week.

As the saying goes "Old Fortran programmers can write Fortran in any
language" so using a newer compiler for Fortran 77 changes nothing
other than some operating system dependence.

You might want to redo things with Fortran 90 array notation and
use the matrix multiply intrinsics as an exercise. If Numerical
Recipes can have (and have had for a long time) a Fortran 90
version then one would expect others to meet even that minimal standard.

By the way, g95 produces exactly the same results as g77 with this
code. If you could donate the code in newer Fortran, please. It would
be my pleasure to compile it and compare timing.

Gfortran has the intent of reproducing G77 on the source that G77
accepts, subject to exceptions over dropped extensions. So that is
hardly very surprising.

There is also the question of the intended audience for an introductory
text and whether that audience should be treated to content which is so
dated.

I am not sure I understand you. Do you mean that NumPy, C, C++ and
ATLAS are outdated?

There is an old saying giving two recipes for swill.

One has a tablespoon of swill and a gallon of fine wine. The other
has a gallon of swill and a tablespoon of fine wine. Both produce
swill.

In a fast skim I noticed some comments on memory issues. I did not
notice comments on the issues of size scaling when the matrix fits in the
cache memory and when it does not. When it does not then is the issue of
subscript order that may or may not be cache friendly. The advice that
good subroutine packages deal with such issues is good. One would like
some indication of the problem they address even if the full technical
nature of the solution is not given. Keeping such a discussion both
accurrate and introductory is not easy.

Well, the goal was learning by doing. One first observe something and
then starts thinking why it is. I guess that it is understandable that
a matrix of 1000x1000 does not fit in the processor cache.

If you are trying to give advice then mentioning the effects of
subscript order on both cache and page hits as sizes grow would
seem to reflect the modern world. Time the filling a large array
in random order, as some problems might suggest, against the
same content in a sequential order.

Best wishes,

Evgenii
http://MatrixProgramming.com


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Relevant Pages

  • Re: Matrix Multiplication
    ... Fortran and I am not sure if I want to learn it. ... One has a tablespoon of swill and a gallon of fine wine. ... subscript order that may or may not be cache friendly. ...
    (sci.math.num-analysis)
  • Re: Matrix Multiplication
    ... author who seems to like to use a 30 year old version of Fortran. ... notice comments on the issues of size scaling when the matrix fits in the ... subscript order that may or may not be cache friendly. ... accurrate and introductory is not easy. ...
    (sci.math.num-analysis)
  • Re: Choice of programming language
    ... Parallel arrays could double your cache ... misses and require an extra register. ... It's been a while since I used FORTRAN. ... <snip the rest> ...
    (sci.math.num-analysis)
  • Re: Matrix Multiplication
    ... I have written an introductory text about matrix multiplication where ... I compare the performance in NumPy, Fortran, C, and C++. ... There is also the question of the intended audience for an introductory ...
    (sci.math.num-analysis)
  • Re: Fortran Code to Pascal Code
    ... williamdiazs wrote: ... While this compiles without any problems, ... Are you accounting for the reversal of subscript order from Fortran to Pascal? ...
    (comp.lang.fortran)