GAMS optimizing assignments

The following fragment shows an unexpected performance problem. I thought all these assignments should be fast (i.e. only over the nonzero elements).

   1  set i /i1*i300/;
   2  alias (i,j,k);
   3   
   4  parameter p(i,j,k);
   5  p(i,i,i) = 3.14;
   6   
   7  parameter p1(i,j,k),p2(i,j,k);
   8   
   9  p1(i,j,k) = -p(i,j,k);
  10  p2(i,j,k)$p(i,j,k) = -p(i,j,k);
  
----      1 ExecInit                 0.000     0.000 SECS      3 Mb 
----      5 Assignment p             0.000     0.000 SECS      4 Mb    300
----      9 Assignment p1            2.683     2.683 SECS      4 Mb    300
----     10 Assignment p2            0.000     2.683 SECS      4 Mb    300

We see here the assignment to p1 is slow (GAMS runs through the carthesian product i x j x k) while the assignment to p2 is fast. I would expect the assignment to p1 to be fast as well.

An assignment of the form
p1(i,j,k) = (-1)*p(i,j,k)
would be optimized by GAMS while
p1(i,j,k) = -1*p(i,j,k)
would be slow again.

The profiler can help you detect these situations and optimize the assignments manually like I did for p2.