how to get any element from a set

GAMS
1

Hi,
For example, if yours variable is H(A) the first element corresponds to H(‘a1’)
Bye

2

Hi
If you want a specific set element, you can also use the ord and card functions:

set 
A/a1,a2/;
parameter h(a);

* first element
h("a1")
h(a)$(ord(a) = 1)

* second element
h("a2") 
h(a)$(ord(a) = 2)

* last element
h(a)$(ord(a) eq card(a))

Cheers
Renger

3

Does GAMS not distinguish capital and lower letters?

True. It does not.

To “populate” a set:

set A /a1,a2/;
set B(A);

B(A)=YES$(ord(A)=2);

display B;
4

Hi Renger,

when I assign an element of a parameter to a scalar, error happens with “Uncontrolled set entered as constant” and “Set for ‘ord’ is not controlled”
Set A /a1,a2/;
parameter h(a) /a1*a2 2/;
scalar y /0/;
y=h(a)$(ord(a) = 1);

Could you please tell where the problem is? Thank you.

Best regards,
Yongning

5

Hi
y is defined as a scalar, so no index. If you write it like you did, Gams expects a set indicator also on the RHS. But this might not what you want, as you set the values for y for all other elements of a to zero:

parameter y(a);

y(a)$(ord(a) =1) = h(a);
display y(a)

You could keep y as a scalar and write the following

loop(a, 
y = h(a)$(ord(a) = 1);
);

or

y = h("a1")

Hope this helps
Cheers
Renger