Re: [Reduce-algebra-developers] Reduce: problem with package linalg

[Rainer S. <rai...@gm...>]

With the latest checkin, svd should no longer hang.

A comparison of the algorithm with the version in the book "Numerical recipes"
showed a misplaced closing paren, causing the algorithm to run endlessly. At the
same time I added an upper limit for the number of iterations. Even if the
computation doesn't converge it will now stop after a while.

The sparse package shows the same error. However, trying its spsvd routine on
some non-square matrices uncovered other problems. I will look into these next.

 Best regards,
   Rainer


On Fri, 23 Feb 2024 at 20:17 -0000, Prof Tony Roberts via Reduce-algebra-de...:

 > Hi,
 >
 > have run into a problem with package lin_alg (and package sparse
 > also has similar issues).  Can anyone fix?
 >
 > Using redcsl (rev 6339) I execute the following script
 >
 > on rounded; print_precision 4$
 > load linalg;
 > a:=mat((-2,3),(5,7));
 > svda:=svd(a);
 > b:=a/3;   svdb:=svd(b);
 > c:=a/2;   svdc:=svd(c);
 > end;
 >
 > To get the two different failures for matrices b and c.
 >
 > 1: in "tmp.txt"$
 >       [-2  3]
 > a := [     ]
 >       [5   7]
 > svda := {
 >           [0.1722   - 0.9851]
 >           [                 ]
 >           [0.9851   0.1722  ]
 >           ,
 >           [8.713    0  ]
 >           [            ]
 >           [  0    3.328]
 >           ,
 >           [0.5257   0.8507  ]
 >           [                 ]
 >           [0.8507   - 0.5257]
 >           }
 >       [ - 0.6667    1  ]
 > b := [                ]
 >       [  1.667    2.333]
 > ***** svd: Non-numeric matrix element at position ( 1 , 1 )
 > Cont? (Y or N)
 > ?y
 >       [ - 1  1.5]
 > c := [         ]
 >       [2.5   3.5]
 >
 > And then redcsl just hangs, and I have to kill the process.  Could
 > someone advise on a work around (for larger matrices).
 >
 > The package sparse also causes similar failure.
 >
 > Tony
 >
 > --
 > ---------------------------------------------------------------------
 > Four books and a toolbox:
 >
 > * (2020) Linear Algebra for the 21st Century
 > Oxford University Press. isbn: 978-0-19-885640-5, 978-0-19-885639-9
 > https://global.oup.com/academic/product/linear-algebra-for-the-21st-century-9780198856399
 >
 > * (2015) Model emergent dynamics in complex systems
 > SIAM, Philadelphia. isbn: 9781611973556.
 > https://epubs.siam.org/doi/10.1137/1.9781611973563
 >
 > * (2009) Elementary calculus of financial mathematics
 > SIAM, Philadelphia. isbn: 978-0-898716-67-2.
 > https://epubs.siam.org/doi/10.1137/1.9780898718225
 >
 > * (1994) A one-dimensional introduction to continuum mechanics
 > World Sci. isbn: 978-981-02-1913-0.
 >
 > * (2020) with John Maclean, and J. E. Bunder; Equation-Free
 > function toolbox for Matlab/Octave.
 > http://github.com/uoa1184615/EquationFreeGit
 >
 > Emeritus Professor A.J. Roberts,  FAustMS
 > School of Mathematical Sciences,  University of Adelaide
 > https://profajroberts.github.io/
 > mailto:Pro...@pr...
 > http://orcid.org/0000-0001-8930-1552
 >
 >
 >
 >
 > _______________________________________________
 > Reduce-algebra-developers mailing list
 > Red...@li...
 > https://lists.sourceforge.net/lists/listinfo/reduce-algebra-developers
 >
 >

   Rainer Schöpf