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Re: [Help-glpk] glpk 4.42 release information

From: Yingjie Lan
Subject: Re: [Help-glpk] glpk 4.42 release information
Date: Thu, 14 Jan 2010 19:47:29 -0800 (PST)

> > Thanks, quickly looked at the
> reference manual and it looks really
> > good. The sensitivity report preamble message has been
> turned off,
> > which is nice. But I'm not sure what would happen if
> you give
> > glp_analyze_coef a none-basic variable?
> This is a trivial case which needs no analysis. For
> example, if
> non-basic variable x have its lower bound active and its
> reduced
> cost, say, 1.23, you cannot decrease the objective
> coefficient more
> than on 1.23; otherwise the reduced cost becomes negative
> and the
> basis becomes dual infeasible (non-optimal).
> >  Similarly, what would happen
> > if you give glp_analyze_bound a basic variable?
> This is also a trivial case, even easier than the previous
> one.
> For example, if primal value of basic variable x is 3.21,
> its lower
> bound cannot be greater and its upper bound cannot be less
> than 3.21;
> otherwise the basis becomes primal infeasible.

Sure, both cases are trivial, I am only not sure what the call would result? 
Would there be some bad consequences of you call that way?

> >  The reference manual
> > does not mention this, it seems to me. BTW, I'm not
> sure how to check
> > if a variable is basic or not, simply checking if the
> value is at one
> > of its bounds is easy but not a reliable way to do
> this.
> glp_get_row_stat/glp_get_col_stat should be used.

Thanks for that one. :)


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