In linear algebra, a definite matrix refers to a square matrix that has specific properties related to the positivity of its quadratic forms. The terminology typically includes several definitions: 1. **Positive Definite Matrix**: A symmetric matrix \( A \) is called positive definite if for all non-zero vectors \( x \), the following holds: \[ x^T A x > 0. \] This implies that all eigenvalues of the matrix are positive.
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A definite matrix is a Hermitian matrix whose associated quadratic form has a fixed sign. Positive and negative semidefinite matrices allow zero as well.