#959 To know which are the inconsistent equations

closed
nobody
5
2009-11-29
2006-07-12
No

Hi,
I have an inconsistent equation system,
I need to know which are the inconsistent equations
when the linsolve command is used. I know that this is
displayed when the flag solve_inconsistent_error is
true, but I need to use this information in a program.

For example,
(%i169) linsolve([a+b=0,a+b=1,a+c=2],[a,c]);
Inconsistent equations: (2)
-- an error. Quitting. To debug this try
debugmode(true);
(%i170)

I need to know that 2 is the inconsistent equation,
Is there any way to know that?
Thank you

Araceli

Discussion

  • Barton Willis
    Barton Willis
    2006-08-14

    Logged In: YES
    user_id=895922

    Without hacking the function solvex (in src/solve), I
    don't think there is a way to get at this information.
    Of course, which equation is is inconsistent is somewhat
    arbitrary: in [x=3,x=6,x=7], which two equations are
    inconsistent?

    Maybe you would like to use the function rank:

    (%i24) load(linearalgebra)$
    (%i25) rank(matrix([6,7],[6,17]));
    (%o25) 2(%i26) rank(matrix([6,7],[6,7]));
    (%o26) 1

     
  • Robert Dodier
    Robert Dodier
    2006-08-26

    • labels: --> Lisp Core - Solving equations
     
  • Logged In: NO

    hi
    (%i12) linsolve([a+b=1,a+c=2],[a,c]);
    (%o12) [a = 1 - b, c = b + 1]
    (%i13) linsolve([a+b=0,a+c=2],[a,c]);
    (%o13) [a = - b, c = b + 2]
    (%i14) linsolve([a+b=0,a+b=1],[a,c]);
    Inconsistent equations: (2)
    -- an error. To debug this try debugmode(true);
    the equations [a+b=0,a+b=1] are contradictory, and if you remove one of them your system has a solution. but look at the system
    linsolve([a=0,c=0,a+c=1],[a,c])
    these three equations are inconsistent but if you pick two of them a unique solution exists. so what are the inconsistent equations?
    in the common case you cannot say these equations of a systems are inconsistent and the rest is consistent. of course an inconsistent system can contain an inconsistent subsystems, but i think how to find out such inconsistent subsystems is a question for a mathematics group and not for a bug report
    guenter

     
  • Dieter Kaiser
    Dieter Kaiser
    2009-11-29

    • status: open --> closed
     
  • Dieter Kaiser
    Dieter Kaiser
    2009-11-29

    I think this is not a bug report, but a support request. Perhaps it is a feature request.
    Closing this bug report as out of date.
    Dieter Kaiser