Re: [Plplot-devel] svd.f = svdcmp from NR

[<jc...@fe...>]

On Friday 26 September 2003 05:56, Alan W. Irwin wrote:
| On 2003-09-26 00:38+0100 Jo=E3o Cardoso wrote:
| > On Thursday 25 September 2003 23:36, Pavel Sakov wrote:
| > |  Hi Folks,
| > |
| > |  I probably should have been more explicit in my message to Joao.
| > |
| > |  I checked svd.f from EISPACK, and this file is equivalent to
| > | svdcmp() from NR. I mean, it is the source of the svd code in NR.
| > | The NR authors did not even bother to rename the variables.
| >
| > Shameful!
|
| Actually not.  They gave full credit in the NR book to prior work,
| and that is all that is required.  That prior work was all free so NR
| could make small changes to the fortran source, convert to C and
| relicense the code in any way they chose.
|
| To avoid that bad license, we just have to steer completely clear of
| both the fortran and C NR versions and go back and rederive what we
| need directly from EISPACK fortran source using f2c.

I'm pretty satisfied with Pavel's approach to solve the problem, as the=20
following highlights from private e-mails show. When I will sync PLplot=20
with Pavel's csa everything will be OK:

   ...
   pavel > However, as you suggested, one can use the original code from=20
           EISPACK, and that is what I have done.
   ...
   pavel > Compared with the previous version of SVD code in csa, most=20
         of the changes were pretty cosmetic.=20
   ...
   pavel > The only thing that arguably was borrowed from NR was the=20
         idea of  rewriting the input matrix A by output matrix U. [jc: =20
         but this is normal practice in other fortran routines, if I=20
         remember correctly]
   ...
   jc > But you will change the NR credits in the source file, asserting   =
=20
         the facts, right?

   pavel > After syncing the code with EISPACK, I changed the credits to=20
         EISPACK.
   ...
   pavel > Correction -- there is a reference to EISPACK Guide in the=20
        SVD chapter.

Does everybody agree?

Joao