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ampl

AMPL: Invalid subscripts

I'm intending to conduct an optimization but I get an error which I cannot find the cause to. The compiler complains about servicetime, startlimit and endlimit not being invalid. In particular the compiler complains in the constraint TimeConstraint that there is no value for servicetime['ORIGINS'].

The constraint in question is:

subject to TimeConstraint {k in H}: sum{i in UNI, j in UNI} servicetime[i]*x[i,j,k] <= 1440;

where:

set ORIGINS;
set DESTINATIONS;
set UNI;
param servicetime{UNI} integer > 0;
var x{UNI,UNI, H} binary;
param startlimit{UNI};
param endlimit{UNI};

the .dat file is:

set ORIGINS := 1 2 3 4 5 6 7;
set DESTINATIONS := 8 9 10 11 12 13 14;
set UNI = ORIGINS union DESTINATIONS;


param: startlimit endlimit  servicetime:=
1   0   1440    360
2   0   1440    360
3   0   1440    360
4   0   1440    360
5   0   1440    360
6   0   1440    120
7   0   1440    120
8   0   1440    360
9   0   1440    360
10  0   1440    360
11  0   1440    360
12  0   1440    360
13  0   1440    120
14  0   1440    120;

I cannot see how this does not work. To me this looks accurate. Hope someone can shed some light into this! Regards,

Solution

  • AMPL data format doesn't permit expressions, so ORIGINS, union and DESTINATIONS are interpreted literally as strings rather than a set expression ORIGINS union DESTINATIONS in the data statement

    set UNI = ORIGINS union DESTINATIONS;

    You can fix this by initializing the set in the declaration in the model file:

    set ORIGINS;
set DESTINATIONS;
set UNI = ORIGINS union DESTINATIONS;
param servicetime{UNI} integer > 0;
...