GAMS sameas problem

I tried a construct that looks like the following code:

sets    cell5m    cell5m_spam ; $gdxin d.gdx $load cell5m cell5m_spam set cellmap(cell5m,cell5m_spam); cellmap(cell5m,cell5m_spam)$sameas(cell5m,cell5m_spam) = yes;   (1)

Basically I take the intersection of the two sets and create a mapping between the two base sets. Unfortunately, the sets are big:

scalars   n_cell5m   n_cell5m_spam ; n_cell5m = card(cell5m); n_cell5m_spam = card(cell5m_spam); display n_cell5m, n_cell5m_spam; ----     23 PARAMETER n_cell5m             =  2294094.000              PARAMETER n_cell5m_spam        =   806882.000

as a result expression (1) takes an extraordinary long time to execute:

----     26 Assignment cellmap    2436.954  2437.032 SECS    383 Mb  806839

I believe the sameas function is just not properly implemented in GAMS. This performance is really not what one would expect.

Of course we can work around this:

sets    cell5m(*)    cell5m_spam(*) ; $gdxin d.gdx $load cell5m cell5m_spam alias (*,u); set intersect(*); intersect(u) = cell5m(u)*cell5m_spam(u); set cellmap(cell5m,cell5m_spam); cellmap(cell5m(intersect),cell5m_spam(intersect)) = yes;

This now executes in much less than a second:

----     27 Assignment intersect     0.187     0.203 SECS    333 Mb  806839 ----     33 Assignment cellmap       0.203     0.406 SECS    358 Mb  806839

Note that we had to change the declarations of the sets a little bit, in order to get this passed the domain checking of GAMS.