1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How to prove that an orthogonal projection matrix is idempotent

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Prove that [P]^2=[P] (that the matrix is idempotent)


    2. Relevant equations



    3. The attempt at a solution

    A(A^T*A)^-1 A^T= (A(A^T*A)^-1 A^T)^2

    Where A^T is the transpose of A. I have no idea.
     
  2. jcsd
  3. Apr 18, 2010 #2

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    What is the relationship between your matrix A and your matrix P?

    Backing up a bit further, what is the definition of an orthogonal projection matrix?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook