Loewner order ($⪯$)

Loewner order, named after the mathematician Charles Loewner, is a way to compare positive definite matrices. In particular, for two symmetric matrices \( A \) and \( B \), we say that \( A \) is less than or equal to \( B \) in the Loewner order, denoted \( A \preceq B \), if the matrix \( B - A \) is positive semidefinite.