(a) A square matrix A is called idempotent if A² = A. Suppose that Xnxp(p < n) is a matrix such that XTX is invertible. Prove that both X(X¹X)-¹XT and In X(X¹X)-¹XT are idempotent. (Hint: use this property of matrix multiplication: (AB)C = A(BC)) (b) For X defined (a), prove the tr(X(X™X)−¹X¹) = p and tr(In - X(X¹X)-¹X¹) n-p =

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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(a) A square matrix A is called idempotent if A²
A. Suppose that Xnxp(p < n) is
a matrix such that XTX is invertible. Prove that both X(X¹X)-¹XT and In
X(X¹X)-¹X¹ are idempotent. (Hint: use this property of matrix multiplication:
(AB)C = A(BC))
(b) For X defined (a), prove the tr(X(XÃX)−¹X¹) = p and tr(In — X(X¹X)−¹X¹) =
n - p
=
Transcribed Image Text:(a) A square matrix A is called idempotent if A² A. Suppose that Xnxp(p < n) is a matrix such that XTX is invertible. Prove that both X(X¹X)-¹XT and In X(X¹X)-¹X¹ are idempotent. (Hint: use this property of matrix multiplication: (AB)C = A(BC)) (b) For X defined (a), prove the tr(X(XÃX)−¹X¹) = p and tr(In — X(X¹X)−¹X¹) = n - p =
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