X indicates whether to build a fire station in a certain area, and C indicates whether it can be reached within 15 minutes between two areas. In this way, it is enough to build a fire station in the second and fourth districts.

Model:

Set:

Area/1.. 6/:x;

link(area，area):t，c；

End set

Data:

t=

4 10 16 28 27 20

10 5 24 32 17 10

16 24 4 12 27 2 1

28 32 12 5 15 25

27 17 27 15 3 14

20 10 2 1 25 14 6;

End data

Calculation:

@for(link:c=@if(t#le# 15， 1，0))；

End calculation

min = @ sum(area:x)；

@ for(area:@ bin(x))；

@for(area(i):@sum(area(j):c(i，j)* x *(I))& gt； = 1);

end