Re: [Help-glpk] [Fwd: Can we set a row with equal upper and lower bound?]

[Xypron]

Hello Andrew,

in glp_simplex (glpk-4.45/src/glpapi06.c) you can find the following code:

         if (row->type == GLP_DB && row->lb >= row->ub)
         {  if (parm->msg_lev >= GLP_MSG_ERR)
               xprintf("glp_simplex: row %d: lb = %g, ub = %g; incorrec"
                  "t bounds\n", i, row->lb, row->ub);

According to the documentation (doc/glpk.pdf) and to the coding in 
routine glp_set_row_bnds() it is allowable for GLP_DB to have lower 
bound == upper bound.

Why would you disallow the the same in glp_simplex?

Best regards

Xypron

On 30.07.2011 05:28, Andrew Makhorin wrote:
> -------- Forwarded Message --------
> From: Wenfei Wu<address@hidden>
> To: address@hidden
> Subject: Can we set a row with equal upper and lower bound?
> Date: Fri, 29 Jul 2011 12:07:35 -0700
>
> Hi, all
>     I am using GLPK now. the version is 4.45. I use it in Cygwin
>     I have a problem.
>     I set up a row with upper bound 0 and lower bound 0, the when I run
> it. Problem appears.
>
>   Code is
>     glp_set_row_bnds(lp, 1, GLP_DB, 0.0, 0.0);
>
>   output is
>    glp_simplex: row 1: lb = 0, ub = 0; incorrect bounds
>
>   Then I change the code
>     glp_set_row_bnds(lp, 1, GLP_DB, 0.0, 0.001);
> and it works.
>
>   Does this mean that we cannot set both bound equal?  But in the GLPK
> reference Manual, on page 13, it says "Bounds of variables can be
> nite as well as innite. Besides, lower and upper bounds can be equal
> to each other."
>
>    Thanks.
>    Wenfei
>
>
>
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