RE: [Help-glpk] The "dual" suffix and sensitivity to how a constraint is expressed in GMPL

[Meketon, Marc]

On reflection, and also after reading Xypron's comments, I agree with you.  
Xypron did enhance the wiki to make this point more visible to other users of 
GLPK.


-----Original Message-----
From: Andrew Makhorin [mailto:address@hidden
Sent: Friday, January 14, 2011 7:26 AM
To: Meketon, Marc
Cc: address@hidden
Subject: RE: [Help-glpk] The "dual" suffix and sensitivity to how a constraint 
is expressed in GMPL

> To me, the only issues are:
> (a) Should GMPL be more clever and check if all the variables are only
> on one  side of the constraint, and if so always place the variables
> on the left-side,  and the constant on the right side, and not
> multiply by -1?  That would create  more intuitive dual variables.

Then it would be unclear what to do, say, with the following constraint:

   x1 + x2 + x3 = x4 + x5 + x6

Besides, in the primal case the rule you suggest is similar to a rule, when, 
for example, a variable declared as x <= 0 is replaced by x >= 0 for the same 
reason.

It seems to me that a "more clever" rule for transforming constraints to the 
standard format would be more confusing.

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