Homepage › Solution manuals › Gilbert Strang › Linear Algebra and Learning from Data › Exercise 3.3.7
Since A = QΛQ−1, so we have Q−1 = Q¯T.
ĀTA = (Q¯Λ¯QT)TQΛQ¯T = QΛ¯TQ¯TQΛQ¯T = QΛ¯ΛQ¯T = Q|Λ|2Q¯T
AĀT = QΛQ¯T(Q¯Λ¯QT)T = QΛQ¯TQΛ¯TQ¯T = QΛΛ¯Q¯T = Q|Λ|2Q¯T
So ${¯A}^TA =A{¯A}^T $