best way to use new qrupdate version?

[John W. Eaton]

On  8-Oct-2009, Jaroslav Hajek wrote:

| in version 1.1, which I intend to release later this year, qrupdate
| will be able to compute rank-1 updates of LU and pivoted LU
| factorizations. The SVN version already has the functionality. I want
| to make the feature again available to Octave via a "luupdate"
| function. The bulk of the code for Octave is already upstream:
| http://hg.savannah.gnu.org/hgweb/octave/rev/6f3ffe11d926
| 
| Because there is 100% backward compatibility, I would like Octave stay
| buildable with qrupdate 1.0, which by now has already spread to
| several distros. The approach I've taken in the above patch is simply
| check for one of the new functions after qrupdate was detected, and
| define an additional macro. But maybe that is not the best idea? Does
| anyone see a better way?
| qrupdate uses a F77-style implicit interface, so there is no header
| file, which could define a versioning symbol.

Couldn't you define a function that returns a version string?  But
even if you did that, I think a version test is not really a
desirable thing to do in a configure script, and doing it with a
function requires running a program, not just linking, so that can
cause trouble for cross compiling (if that even matters for us).

| An alternative is to make qrupdate 1.1 a requirement for Octave 3.4,
| but it seems nice to support the old version if it's compatible.

I guess the choice is yours.  Qrupdate is small and easy to build
though, isn't it?  So it would not be a big burden to require the new
version.  OTOH, if the older version will work (possibly with some
loss of functionality) then continuing to allow its use would be OK
with me.

To check in configure, you could do something like this (untested):

save_LIBS="$LIBS"
LIBS="$BLAS_LIBS $FLIBS $LIBS"
OCTAVE_CHECK_LIBRARY(qrupdate, qrupdate,
  [qrupdate not found.  The QR & Cholesky updating functions will be slow.],
  [],
  [F77_FUNC(sqr1up,SQR1UP)],
  [], [don't use qrupdate, disable QR & Cholesky updating functions],
  [warn_qrupdate=
   AC_CHECK_FUNCS([F77_FUNC(other_qrupdate_fcn,OTHER_QRUPDATE_FCN)],
    [AC_DEFINE(HAVE_OTHER_QRUPDATE_FCN, 1)],
    [warn_qrupdate="other_qrupdate_fcn missing; some loss of functionality"])])
LIBS="$save_LIBS"

jwe