In functional analysis and linear algebra, a **normal operator** is a bounded linear operator \( T \) on a Hilbert space that commutes with its adjoint. Specifically, an operator \( T \) is said to be normal if it satisfies the condition: \[ T^* T = T T^* \] where \( T^* \) is the adjoint of \( T \). ### Key Properties of Normal Operators 1.
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An operator is normal when . Equivalently,for every ; the converse follows by polarizing the quadratic form of the self-adjoint commutator .