Just a somewhat pedantic comment on details of notation first -- If the matrix is 1x5, it would be
instead, a row vector, not column as given above. For addressing a vector it won't matter much, but is quite important to have orientation correct if were 2D instead and also for things like matrix multiplication, etc.
Anyways, tutorial aside, if the size is always 5 elements, then >4 elements being zero is equivalent to
because >4 ==> 5 which is the full size of the vector.
Or if the size is variable or the criterion is for some number other than all, then use
where n is the number of nonzero elements required (1 in the above case).