Re: improved QR & Cholesky updating

[John W. Eaton]

On 21-Jan-2009, Jaroslav Hajek wrote:

| Sorry, this should have been part of the patch, but somehow I forgot
| to do the last refresh (also sorry for the message).
| It's now uploaded. fsolve will simply check for qrupdate at first
| start, and if not found, it will update the qr factorization by
| recalculation. For large systems, of course, that's going to be much
| slower, but will work.
| 
| I intend to do the same thing anywhere the updating routines will be
| used (due to their nature, they can be always replaced). That's why I
| disabled their compiling entirely when qrupdate is not present - so
| that their presence can be checked with the "exist" function.

Instead of

  persistent have_qrupdate = exist ('qrupdate') == 5;

  [...]

  ## Update the QR factorization.
  if (have_qrupdate)
    [q, r] = qrupdate (q, r, u, v);
  else
    [q, r] = qr (q*r + u*v');
  endif

in fsolve.m and every other function that might use qrupdate, why not
check HAVE_QRUPDATE in the QR::update functions and do this operation
there?  Then the check would only have to occur in one place rather
than in every part of Octave that uses qrupdate.

jwe