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Re: [Help-glpk] Strange Error with if/then/else

From: Jonathan Klein
Subject: Re: [Help-glpk] Strange Error with if/then/else
Date: Sat, 05 Apr 2008 17:36:30 +0000
User-agent: Thunderbird 2.0.0.12 (Windows/20080213) 
Hi,
the short example was just du have an minimal example where the error
occurs.
I managed it to rewrite my Problem to something like this:

maximize z: sum{i in STUDENT, l in GROUP, k in COURSE, j in CHOICE}
                        if k==Student_Choice[i, j]
                        then StudentDistribution[i,k,l] * Satisfaction[j]
                        else 0;

which has the same effect, but was no variable in the test sentence.
But is there any good reason why i cant have a varaible in there?

Jonathan


Leandro Barcelos schrieb:

correcting...

You can't put the variable in the test sentence of the if-then-else.
On Sat, Apr 5, 2008 at 2:13 PM, Leandro Barcelos <address@hidden <mailto:address@hidden>> wrote: 

    Jonathan,

    Try:
    maximize Anzahl : sum{i in PEOPLE} x[i];

    That's the same.

    The problem with your equation is that you can't put if-then-else in
    a linear equation

    cya



    On Sat, Apr 5, 2008 at 10:36 AM, Jonathan Klein
    <address@hidden <mailto:address@hidden>> wrote:

        Hi,

        i havbe a very simple Problem like this:

        set PEOPLE;
        var x{i in PEOPLE} binary;
        maximize Anzahl : sum{i in PEOPLE} (if x[i]==1 then 1 else 0);
        data;
        set LEUTE:=Hans Joachen Peter Klaus;
        end;

        And i get the Error: operator preceding == has invalid type

        I know, that this problem doesn't make sense, but i have i
        somewhat more complex problem in wich i get the same error:




        # Berufsinformationstag

        set STUDENT;#i
        set CHOICE;#j
        set COURSE;#k
        set GROUP;#l

        param Student_Choice {i in STUDENT, j in CHOICE} symbolic in
        COURSE;# Welcher Schüler welche Wünsche hat
        #param Course_Minimum {k in COURSE};#Wie viele Schüler eine
        Veranstaltung minimal braucht
        #param Course_Maximum {k in COURSE};#Wie viele Schüler eine
        Veranstaltung haben darf
        param Satisfaction {j in CHOICE};#für jeden wunsch die Menge,
        wie glücklich er ist


        var TimeTable{k in COURSE, l in GROUP}, binary;
        var StudentDistribution {i in STUDENT, k in COURSE, l in GROUP}
        binary ;

        # wenn sich der schüler die aktuelle veranstaltung wünscht und
        in der veranstaltung in dieser gruppe ist
        maximize z: sum{i in STUDENT, l in GROUP, k in COURSE, j in CHOICE}
                               (if 1==StudentDistribution[i,k,l]
                               and k==Student_Choice[i, j]
                               then Satisfaction[k] else 0);





        So i have Students that are in different Courses, in 1 Course
        per Group. They coose 6 Courses and will be in 4 (1 in each
        group). If they are in a grout that the have choosen, they are
        happy.
        So i have to check for every Choice of every Student in every
        Course in every Group if the student is in this course in this
        group and if he had choosen it. If so, he gets as much happiness
        as his choice had importance.

        At the end i need to know form every Student in which courses he
        ist an which courses in which group have to take place, so i
        have choosen the binary variables.

        I dont konw why the types should not match, because
        StudentDistribution ist binary, so i can only be 0 or 1 an
        Student_Choice has to be a COURSE.

        I studiet the language reference manual for a long time and
        looked at many examples with if/then/else but i still have no
        idea what i'm doing wrong.

        PS: I use C++ for 5 years now, but im relativly new to GNU
        MathProg :(

        I would be very gald for every help.

        Jonathan


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-- Leandro B. Barcelos 



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Leandro B. Barcelos
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