the part that is confusing you here is actually just [[1,2,3] [4,5,6]]. this is syntax for constructing a matrix (as opposed to [[1,2,3], [4,5,6]] with a comma

the part that is confusing you here is actually just [[1,2,3] [4,5,6]]. this is syntax for constructing a matrix (as opposed to [[1,2,3], [4,5,6]] with a comma which makes a vector of vectors). Julia has first class support for n dimensional arrays which is very useful for scientific/mathy code