Optimize Expressions

ETL is able to optimize some expressions if it can be resolved more efficienty. For instance, this expression:

C = (A * 1.0) * (B + 0.0);

is exactly the same as:

C = A * B;

but the second version saves multiplications, additions and two matrix copy.

In ETL, you can use the function opt to ensure that an expression will be optimized before being evaluated:

C = opt((A * 1.0) * (B + 0.0));

In this case, it will be execute directly as a matrix multiplication of A and B.

While the gain can be very noticeable, it has a great impact on compilation time. It is in fact combinatorial in the number of possible expressions in ETL. If you use opt on complex expressions, compilation of the expression can be several orders of magnitude slower. This is why optimization is not enabled by default in ETL.