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Re: [Bug-glpk] GLPK 4.44: display statement above solve

From: Andrew Makhorin
Subject: Re: [Bug-glpk] GLPK 4.44: display statement above solve
Date: Mon, 7 Jun 2010 03:46:54 +0400

> in GLPK 4.44 the display statement does not work for
> constraints and variables without suffix when used above
> the solve statement.

> invalid reference to status, primal value, or dual value of
> constraint demand above solve statement
> Context: ...) in K } x [ i , j ] >= b [ j ] ; display demand [ '...' ] ;

> invalid reference to variable x above solve statement
> Context:  sum { ( i , j ) in K } x [ i , j ] >= b [ j ] ; display x ;

> According to doc/gmpl.pdf, version 4.42 accompanying GLPK 4.44
> display statements above the solve statement are allowable:

> "Note that if the display statement is used above the solve statement
> and the item is a variable, its displayed "value" means "elemental
> variable", not a numeric value, which the variable could have in some
> solution obtained by the solver. To display a numeric value of a variable
> the display statement should be used below the solve statement.
> Analogously, if the item is a constraint or objective, its "value"
> means "elemental constraint" or "elemental objective", not a numeric
> value."

Displaying variables and constraints above the solve statement doesn't have
much sense. I included this feature only to check which elemental variables
and constraints are actually stored in corresponding arrays. However, you can
obtain this information from the problem instance generated, say, with using
--wlp option.

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