# Row-Reduced Echelon Forms

1. Sep 18, 2007

### innightmare

I am having problems with understanding the whole concept/how to compute the row-reduced echelon form.

2. Sep 18, 2007

### bel

A matrix remains unchanged after going through the elementary row operations, so the whole concept is to keep on multiplying rows and adding (or subtracting) them from other rows to give an upper triangular matrix.

3. Sep 18, 2007

### innightmare

The book that i have doesnt give examples nor is it clear about the upper triangular matrix. Can you PLEASE explain whats an upper triangular matrix?

4. Sep 18, 2007

### bel

It is just a matrix $$\{a_{ij}\}$$ where the terms for which $$i$$ is bigger than $$j$$ are all zero.

5. Sep 18, 2007

### innightmare

yes, but i thought you changed your matix after changing the equation pertaining to it

6. Sep 18, 2007

### bel

Yes it does, generally, but not if you change the system of equations in strict accordance with the elementary row operations. Chapter three of Wylie's and Barrett's Advanced Engineering Mathematics (sixth edition) has proofs, and most university libraries have that book, I think.

7. Sep 19, 2007

### ice109

just write out a system of equations, any system which you know is consistent and solve it. now write out the matrix for it and get it into rrref form and you'll see that you're performing the same operation you've just taken out the xs

8. Sep 20, 2007

### HallsofIvy

Staff Emeritus
An upper triangular matrix is a matrix that has only zeros below the "main diagonal".
In other words, the non-zero entries form a triangle and it is above the diagonal.