Re: [vox-tech] numerical packages in C?

[Peter Jay Salzman <p@dirac.orMAPSg>]

mark, thanks for the tip.  if nobody has the CD, i plan on taking a trip to
the library to check it out.

rhonda and i wrote a program to invert a matrix using gauss-jordan with full
pivoting (searching both rows and columns for the optimal pivot point, and
switching both rows and columns).

i learned A LOT from the excersize.   for example, let A be a square matrix.
let R(1,2) be a transformation that switches rows 1 and 2.  C(1,2) does the
same except with columns.

suppose you want to find the inverse of A, but instead find the inverse of

        M = R(1,2)C(2,3)R(1,5)C(11,2)C(2,3)A

then you invert M to get Minv.  to get Ainv...

        Ainv = C(1,2)R(2,3)C(1,5)R(11,2)R(2,3)Minv

this is the opposite of the "shoes and socks" property, but it makes perfect
sense when you consider how matrix multiplication works.

anyway, i learned lots of little stuff like this that i never knew before.

i plan on writing some routines like this (eigenvalue solver, etc) and make
them into a static library.

pete


On Sun 14 Jan 01,  3:13 PM, Mark Kim said: 
> On Sat, 13 Jan 2001, Peter Jay Salzman wrote:
> 
> > is there a C equivalent of LAPACK and BLAS (which i understand to be
> > fortran)?
> 
> There was an article on Dr. Dobb's Journal (or was it C/C++ Users'
> Journal?... pretty sure it was DDJ) about a couple years ago about a
> numerical C library that outperformed FORTRAN.  The author of the article
> (who also authored the library) was trying to show how modern C compilers
> can outperform FORTRAN with a little tweak.  I don't exactly remember
> which issue, but it must have been somewhere between late 1997 and early
> 1999.  I'm pretty sure the article covered multiple compilers,
> including gcc.  Can someone with the DDJ CD do a search for "C and
> FORTRAN"?
> 
> -Mark
> 
> ---
> Mark K. Kim
> http://www.cbreak.org/mark/
> PGP key available upon request.
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