## Undertanding an example with binary variables

Jtrent
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### Undertanding an example with binary variables

Hello all

I'm studying the example of GAMS library: Enumerate all Feasible Basic Solutions of the Transportation Problem (ALLBASES,SEQ=396)
In the description they mention this statement: We reformulate in standard form use binary variables to determine if a variable belongs to the basis or not.
I don't quite understand what belongs to the basis means... I do understand the formulation but I don't get the purpose of it...

May someone give me a hand on this doubt ...
This is the formulation of the "Basis" :
* Basis definition
Variables
xind(i,j) x basis indicator
sslind(i) sslack basis indicator
dslind(j) dslack basis indicator
Binary Variable xind, sslind, dslind;

Equations
defbasis basis definition
defximp(i,j) xind=0 => x=0
defsslimp(i) sslind=0 => ssl=0
defdslimp(j) dslind=0 => dsl=0;

defbasis .. card(i) + card(j) =e=
sum((i,j), xind(i,j)) + sum(i, sslind(i)) + sum(j, dslind(j));

defximp(i,j) .. x(i,j) =l= min(a(i),b(j))*xind(i,j);
defsslimp(i) .. sslack(i) =l= a(i)*sslind(i);
defdslimp(j) .. dslack(j) =l= b(j)*dslind(j);