On Thu, 2018-02-15 at 21:21 +0100, Heinrich Schuchardt wrote: > Hello Giovanni, > > please, read doc/gmpl.pdf which comes with the GLPK source. > > The <<>> syntax may exist in AMPL but it does not exist in GMPL. > > Depending on your piecewise linear function being concave or convex > you can replace it with some linear constraints or you will have to > introduce extra binary variables.
Please see http://en.wikibooks.org/wiki/GLPK/Modeling_tips . > > Best regards > > Heinrich > > Am 15.02.18, 21:10, Giovanni Di Stasi <[email protected]> > schrieb: > I am trying to use such functions but I get a syntax error. > In particular, this is my program, taken by the following book > chapter: > > > https://ampl.com/BOOK/CHAPTERS/20-piecewise.pdf > > > > set ORIG; # origins > set DEST; # destinations > param supply {ORIG} >= 0; # amounts available at origins > param demand {DEST} >= 0; # amounts required at destinations > check: sum {i in ORIG} supply[i] = sum {j in DEST} demand[j]; > param rate1 {i in ORIG, j in DEST} >= 0; > param rate2 {i in ORIG, j in DEST} >= rate1[i,j]; > param rate3 {i in ORIG, j in DEST} >= rate2[i,j]; > param limit1 {i in ORIG, j in DEST} > 0; > param limit2 {i in ORIG, j in DEST} > limit1[i,j]; > var Trans {ORIG,DEST} >= 0; # units to be shipped > minimize Total_Cost: sum {i in ORIG, j in DEST} > <<limit1[i,j], limit2[i,j]; > rate1[i,j], rate2[i,j], rate3[i,j]>> Trans[i,j]; > subject to Supply {i in ORIG}: > sum {j in DEST} Trans[i,j] = supply[i]; > subject to Demand {j in DEST}: > sum {i in ORIG} Trans[i,j] = demand[j]; > > > > > When I try to make glpk parse it, I get the following error: > > > glpsol --model glpk/Test --data /tmp/DATAg5ZQ0L > -w /tmp/OUTXlm0ST > GLPSOL: GLPK LP/MIP Solver, v4.61 > Parameter(s) specified in the command line: > --model glpk/Test --data /tmp/DATAg5ZQ0L -w /tmp/OUTXlm0ST > Reading model section from glpk/Test... > glpk/Test:14: syntax error in expression > Context: ...>= 0 ; minimize Total_Cost : sum { i in ORIG , j > in DEST } < > MathProg model processing error > > > > > I really have no clue as of now. > > > Thanks > > > > > > _______________________________________________ Help-glpk > mailing list [email protected] > https://lists.gnu.org/mailman/listinfo/help-glpk > _______________________________________________ > Help-glpk mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/help-glpk _______________________________________________ Help-glpk mailing list [email protected] https://lists.gnu.org/mailman/listinfo/help-glpk
