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

From: Andrew Makhorin
Subject: Re: [Help-glpk] [Fwd: Can we set a row with equal upper and lower bound?]
Date: Sun, 31 Jul 2011 15:43:29 +0400

> 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?

Glp_set_row/col_bnds does not check bounds at all; for example, one can
specify a lower bound which is greater than upper one. This is made
intentionally to allow setting lower and upper bounds independently on
each other. However, glp_simplex and other solvers requires all bounds
to be correct.

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