A prime number is a positive integer that cannot be divisible by other positive integers except 1 and itself.

Let f be a real symmetric bilinear function with f(α, α)>0 for any vector α∈V, and it is said that f is positive definite. A time symmetric matrix A with the same property, that is, for any real nonzero column matrix X, a matrix with xtax >:0 is also called positive definite.