I tried to compare the arraymath extension suggested in a comment with my plpgsql solution from the last post.
PostgreSQL was 9.5rc1 on Ubuntu 14.04 LTS.
create extension arraymath;
No problems so far, but...
select array(select random() from generate_series(1,1000000)) @+ array(select random() from generate_series(1,1000000));
NOTICE: Hello from ArrayMath 1.0
********** Error **********
Whereas the plpgsql code does the addition of two one million element vectors in 1.2 seconds.
Interestingly this works:
SELECT ARRAY[1,2,3,4,5,6,7,8] @+ ARRAY[1,2,3,4,5,6,7,8];
While this crashes:
SELECT ARRAY[1,2,3,4,5,6,7,8,9] @+ ARRAY[1,2,3,4,5,6,7,8,9];
So arraymath seems to fail with vectors larger than 8 elements. Probably only on 9.5, but I couldn't get it to work properly.