semidefiniittisyys
Semidefiniittisyys is a property of matrices and quadratic forms. A real symmetric matrix A is said to be positive semidefinite if for every non-zero real vector x, the quadratic form x^T Ax is non-negative. This means that x^T Ax >= 0 for all x. A matrix that is positive semidefinite is also said to be negative semidefinite if the quadratic form x^T Ax is non-positive for all non-zero real vectors x. This means that x^T Ax <= 0 for all x.
A matrix that is neither positive semidefinite nor negative semidefinite is indefinite. The concept of semidefiniteness
There are several ways to check for semidefiniteness. One common method is to examine the eigenvalues of