The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

Definition of an Identity Matrix

Date: 08/09/99 at 12:00:59
From: noor
Subject: Identity Matrix

Can someone please tell me what is the definition of an identity 
matrix? Which of the following would be an identity matrix?

  -1   2              1   -3              -2    2
   3  -4             -5    7               3   -4
                                          -5    6

Date: 08/10/99 at 01:28:11
From: Doctor Rob
Subject: Re: Identity Matrix

None of these is an identity matrix. An identity matrix must be a 
square. All the off-diagonal entries are zero. Finally, the entries on 
the main diagonal are all ones. For example,

   [1  0  0]
   [0  1  0]
   [0  0  1]

- Doctor Rob, The Math Forum   
Associated Topics:
High School Definitions
High School Linear Algebra

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.