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!

Pivoting (Gaussian elimination)

  1. Feb 23, 2017 #1
    1. The problem statement, all variables and given/known data

    x1 + 2x2 = 9 ,
    6x1 + 6x2 -8x3 = 1 ,
    -3x2 +x3 = 0

    Here's a question from my book . I'm asked to find the x1 , x2 and x3 by using the gaussian elimination with pivoting .


    2. Relevant equations


    3. The attempt at a solution

    Pls refer to this thread for the lecturer's method
    https://www.physicsforums.com/threads/gaussian-elimination-pivoting.905132/#post-5699372

    By using the lecturer's method ( circle out the max element in each column ) , I found that all the greatest element lies in 6x1+ 6x2 - 8x3 = 1 ...
    So , how could all the largest element lies in the same row ?
     
    Last edited: Feb 23, 2017
  2. jcsd
  3. Feb 23, 2017 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Fate, coincidence, exercise composer's whim, anything. It happens. You just play along and swap rows 1 and 2 -- by the book . :wink:
     
  4. Feb 23, 2017 #3

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    And if we are going to do much more of this, you should learn a bit of ##\LaTeX## instead of making photos. It's fun and pretty easy.
    Code (LaTeX):

    $$\begin{pmatrix}
    1 & 2& 0 & 9 \\
    6 & 6 & -8 & 1 \\
    0 & -3 & 1 & 0
    \end {pmatrix
    } $
    $
     
    gives you
    $$\begin{pmatrix}
    1 & 2& 0 & 9 \\
    6 & 6 & -8 & 1 \\
    0 & -3 & 1 & 0
    \end {pmatrix} $$
     
  5. Feb 23, 2017 #4
    So
    So , I cant use the lecturer's method to do this question ?
     
  6. Feb 23, 2017 #5

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    In the thread

    https://www.physicsforums.com/threads/gaussian-elimination.904589/

    I gave you a detailed explanation of Gaussian elimination and pivoting, along with the main reasons that pivoting is performed at all. You should go back and actually READ that explantion.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Pivoting (Gaussian elimination)
  1. Gaussian elimination (Replies: 2)

  2. Gaussian elimination (Replies: 3)

  3. Gaussian elimination (Replies: 10)

  4. Gaussian elimination (Replies: 13)

Loading...