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Posted 03-09-2015 07:10 AM
(1145 views)

Hello,

I would appreciate help concerning the following part of SAS/OR(R) 9.3 User’s Guide: Mathematical Programming Legacy Procedures. It's about the balancing restriction of a transport problem.

con balance {i in NODES}: sum {<(i),j> in ARCS} Flow[i,j]

- sum {<j,(i)> in ARCS} Flow[j,i] = _sd_*;*

num infinity = min {r in {}} r;

/* change equality constraint to le constraint for supply nodes */

for {i in NODES: _sd_* > 0} balance .lb = -infinity;*

The mathematical reason to change to "less or equal than" is clear. What I don't get is the syntax of min {r in {}} r. Is it a constant or a variable? Are there simpler formulations?

Thanks & kind regards

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That expression is the minimum of the empty set and is a constant that is equal to the largest double-precision floating-point number (8-bytes) that is representable on your computer. Later versions of the documentation (starting in 13.1) use instead the simpler but equivalent constant('BIG'):

SAS/OR(R) 13.1 User's Guide: Mathematical Programming Legacy Procedures

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That expression is the minimum of the empty set and is a constant that is equal to the largest double-precision floating-point number (8-bytes) that is representable on your computer. Later versions of the documentation (starting in 13.1) use instead the simpler but equivalent constant('BIG'):

SAS/OR(R) 13.1 User's Guide: Mathematical Programming Legacy Procedures

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Hi user24feb - are you referring to generalized network flow, specifically?

All of the network algorithms available in OPTNET are also available in OPTMODEL. A specific solver for generalized networks is not available in either product. Generalized networks are easily solved by the standard simplex algorithms (e.g., dual simpex) available in OPTMODEL (or OPTLP).

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