Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I would like to know what is a idempotent matrix? Also, which invertible matrices are also idempotent and can a matrix be nilpotent and idempotent at the same time?

share|improve this question

1 Answer 1

up vote 3 down vote accepted
  1. In algebra, an idempotent matrix is a matrix which, when multiplied by itself, yields itself. (guess where this is from...)

  2. With the exception of the identity matrix, an idempotent matrix is singular...

  3. Does the zero matrix count?

share|improve this answer
3  
In fact, there are exactly three kinds of idempotant matrices: the unit matrix (invertible), the zero matrix (nilpotent) and all others (neither). –  Johannes Kloos Oct 9 '12 at 9:17

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.