问题
I'm learning AMPL so that I can use it some time later in my programs. I have a small question though that I couldn't find its answer yet.
Suppose I have a set, this set will contain some subsets, those subsets may differ in their dimensions. For example:
set x:= (a,b,c) (a,c) (d,t,r,e,s);
and so on ..
Now I want to write a constraint which will have to deal with all elements in each subset (similar to a loop that will iterate between a,b, and c in the first subset, a and c in the second and so on). The problem is that we don't know the size of each so we can't use the following:
set x dimen 3;
subject to constraint {(i,j,k) in x}: "some constraint";
data;
set x:= (a,b,c) (a,c) (d,t,r,e,s);
Is there a way to do so? If yes, can you please provide me with some sample code or links to learn from? Thanks in advance. Your help is appreciated :D
回答1:
You can have an indexed set in AMPL which is kind of "set of sets", but all elements of it should have the same dimension:
set S;
set T{S} dimen 3; # indexed set with all elements of dimension 3 (triples).
However, you can achieve the same effect with parameters:
set V ordered;
param values{V} symbolic;
# Indices in values where each subset starts.
set Indices ordered;
data;
param:
V: values :=
1 a
2 b
3 c
4 a
5 c
6 d
7 t
8 r
9 e
10 s;
set Indices := 1 4 6 11;
print {i in Indices: i != last(Indices)}: {j in i .. next(i) - 1} values[j];
Running this code will print
a b c
a c
d t r e s
来源：https://stackoverflow.com/questions/24727818/ampl-variable-size-set-iteration