n (analysis) A
function denoted ||
v|| that
maps a
vector v to a
non-negative value such that ||
cv|| = |
c|.||
v||, where
c is a
scalar, and ||
v +
w|| ≤ ||
v|| + ||
w|| (the
triangle inequality); the condition that ||
v|| = 0 implies that
v = 0 is not required, but when it holds, the semi-norm is a
norm.