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[Bug-glpk] min{} over empty set; result undefined


From: xypron
Subject: [Bug-glpk] min{} over empty set; result undefined
Date: Thu, 18 Dec 2008 12:09:52 -0800 (PST)

Hello Andrew,

I received the error
min{} over empty set; result undefined
for the following statement.

param ti{i in O} := max( ti0[i] , min( ta0[i], min{(i,j) in V diff I }
ti0[j]) - d[i] );

Currently for operations over sets in GLPK the following definitions have
been made:
prod{i in {}} i = 1;
sum{i in {}} = 0;
because 1 and 0 are the neutral elements for the operations * and +.

It would be useful to add by definition:
max{i in {}} i = -DBL_MAX; # -infinity
min{i in {}} i =  DBL_MAX; # infinity
because -infinity and infinity are the neutral elements for the operations
max and min.

This can save using "if" expressions in cases as the one above.

Best regards

Xypron
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