If same size,
tmp=[zal1, zal2, zal3, agg1, zgg2, zgg3 ];
maxz=max(tmp(:));
minz=min(tmp(:));
Unfortunate can't use the (:) after the concatenation to avoid the temporary although since there are two operations it saves building twice as I doubt that the optimizer would figure out the optimization on its own.
ADDENDUM:
The whole problem illustrates why would be better, perhaps to rearrange the data structure to use cell arrays or named structures or higher dimension arrays instead of generating a series of sequentially-named variables. Then could eliminate the need to manipulate the separate variables explicitly.
ADDENDUM 2:
tmp=[zal1(:) zal2(:) zal3(:) agg1(:) zgg2(:) zgg3(:)];
gets the vector at the first go which may make a tiny speedup compared to above.
