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Reduced row echelon form of a square matrix 
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#1
Nov1212, 12:41 AM

P: 783

I am wondering about the relation betwen RRE forms and identity matrices. Consider the reduced row echelon form of any square matrix. Must this reduced row echelon form of the matrix necessarily be an identity matrix?
I would suppose yes, but can this fact be proven? Could anyone provide an outline of the proof, or provide the link? Thanks much. BiP 


#2
Nov1212, 03:36 AM

P: 345

In general, a square matrix A is row equivalent to (i.e. its RRE is) the identity matrix of he same size if and only if A is invertible. 


#3
Nov1212, 05:14 PM

P: 783

BiP 


#4
Nov1212, 07:00 PM

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P: 7,150

Reduced row echelon form of a square matrix
$$\begin{pmatrix}1 & 1 \\ 1 & 1\end{pmatrix}$$ 


#5
Nov1212, 07:52 PM

P: 783

BiP 


#6
Nov1212, 08:04 PM

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P: 7,150

Of course it's not in RRE form!
You asked if a square matrix with no zero rows always has an identity matrix for its RRE. That matrix has no zero rows. Reduce that matrix to RRE form and see what you get. If you do that yourself, you might see WHY your idea is wrong (and even discover the right idea), which is more useful than just being told "your idea is wrong". 


#7
Nov1212, 08:05 PM

P: 350

AlephZero is saying to start with that matrix and then do row operations to put it into RRE form. You will find that you end up with a matrix that is not the identity matrix. Since the given matrix has no zero rows, it is a counter example to your modified question.



#8
Nov1212, 08:29 PM

P: 783

I see! Thanks!! The reduction gave me $$\begin{pmatrix}1 & 1 \\ 0 & 0\end{pmatrix}$$
What about if the RRE form of the matrix is a square matrix with no zero rows? In that case is the RRE form become an identity matrix? BiP 


#9
Nov1312, 10:00 AM

P: 345




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