<Tr> <Td> N </Td> <Td> N (\ displaystyle \ mathbb (N)) \ mathbb (N) N (\ displaystyle \ mathbf (N)) \ mathbf (N) </Td> <Td> natural numbers the (set of) natural numbers numbers </Td> <Td> N means either (0, 1, 2, 3, ...) or (1, 2, 3, ...). The choice depends on the area of mathematics being studied; e.g. number theorists prefer the latter; analysts, set theorists and computer scientists prefer the former . To avoid confusion, always check an author's definition of N . Set theorists often use the notation ω (for least infinite ordinal) to denote the set of natural numbers (including zero), along with the standard ordering relation ≤ . </Td> <Td> N = (a: a ∈ Z) or N = (a> 0: a ∈ Z) </Td> </Tr> <Tr> <Td> ○ </Td> <Td> ∘ (\ displaystyle \ circ) \ circ </Td> <Td> Hadamard product entrywise product linear algebra </Td> <Td> For two matrices (or vectors) of the same dimensions A, B ∈ R m × n (\ displaystyle A, B \ in (\ mathbb (R)) ^ (m \ times n)) the Hadamard product is a matrix of the same dimensions A ∘ B ∈ R m × n (\ displaystyle A \ circ B \ in (\ mathbb (R)) ^ (m \ times n)) with elements given by (A ∘ B) i, j = (A) i, j ⋅ (B) i, j (\ displaystyle (A \ circ B) _ (i, j) = (A) _ (i, j) \ cdot (B) _ (i, j)). </Td> <Td> (1 2 2 4) ∘ (1 2 0 0) = (1 4 0 0) (\ displaystyle (\ begin (bmatrix) 1&2 \ \ 2&4 \ \ \ end (bmatrix)) \ circ (\ begin (bmatrix) 1&2 \ \ 0&0 \ \ \ end (bmatrix)) = (\ begin (bmatrix) 1&4 \ \ 0&0 \ \ \ end (bmatrix))) </Td> </Tr> <Tr> <Td> ∘ </Td> <Td> ∘ (\ displaystyle \ circ) \ circ </Td> <Td> function composition composed with set theory </Td> <Td> f ∘ g is the function such that (f ∘ g) (x) = f (g (x)). </Td> <Td> if f (x): = 2x, and g (x): = x + 3, then (f ∘ g) (x) = 2 (x + 3). </Td> </Tr> <Tr> <Td> O </Td> <Td> O (\ displaystyle O) O </Td> <Td> Big O notation big - oh of Computational complexity theory </Td> <Td> The Big O notation describes the limiting behavior of a function, when the argument tends towards a particular value or infinity . </Td> <Td> If f (x) = 6x − 2x + 5 and g (x) = x, then f (x) = O (g (x)) as x → ∞ (\ displaystyle f (x) = O (g (x)) (\ mbox (as)) x \ to \ infty \,) </Td> </Tr>

What is the meaning of this symbol #