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Gaussian Elimination HELP!!!!

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  • 20-10-2003 2:13pm
    #1
    MR DAZ
    Registered Users Posts: 799 ✭✭✭


    Lads,

    I need help with the following gaussian Elimination:

    a + 3b - 2c + 3d = 2
    4a + 12b -8c +14d = 6
    -2a -6b + 4c +d = -11
    3a + 9b - 6c + 5d = 10

    I cant seem to get it to work out....would really appreciate any help on this.

    :confused:

    thanks again


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    #2
    Kold
    Registered Users Posts: 12,778 ✭✭✭✭Kold


    Drop to pass :D


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    #3
    MR DAZ
    Registered Users Posts: 799 ✭✭✭MR DAZ


    Kold..less of your f+%king sarcasim please


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    #4
    Boston
    Closed Accounts Posts: 17,163 ✭✭✭✭Boston


    first off i didn't think this was on the leaving cert, so your un likely to get an answer here. Secoundly i went through it myself and its difinitly fudged as far as i can see. Remember to every linear equation there are 1) No solutions: 2) a single uniquesolution or 3) infinite solutions.

    this seems to have no solutions as when you do row reduction you get some very contradictory answers. Less you what, i'll look at it more deaply and get back to you tomorrow.


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    #5
    MR DAZ
    Registered Users Posts: 799 ✭✭✭MR DAZ


    Thanks boston....

    I am actually stufying for a diploma in Information Technology (1st year)

    This question is on the sample paper, but i couldnt get it to work out, i kept getting all zero's on the top line ????


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    #6
    MR DAZ
    Registered Users Posts: 799 ✭✭✭MR DAZ


    DOH !!! Studying


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    #7
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 91,761 Mod ✭✭✭✭Capt'n Midnight


    try the maths forum http://www.boards.ie/vbulletin/forumdisplay.php?s=&forumid=380 :)


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    #8
    Boston
    Closed Accounts Posts: 17,163 ✭✭✭✭Boston


    Originally posted by MR DAZ
    Thanks boston....

    I am actually stufying for a diploma in Information Technology (1st year)

    This question is on the sample paper, but i couldnt get it to work out, i kept getting all zero's on the top line ????

    it that case theres probably nothing wrong with the question just the lecturer trying to show you that sometimes there is no solution, mine did the same thing


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    #9
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 91,761 Mod ✭✭✭✭Capt'n Midnight


    You can only solve the equations if they are not based on each other. If you have N variables then you need N independent equations.

    If you rewrite them all as expressions = 12a then you will remove the first variable and have expressions in terms of b,c,d


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    #10
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 91,761 Mod ✭✭✭✭Capt'n Midnight 


      a +  3b - 2c +  3d =   2
 4a + 12b - 8c + 14d =   6
-2a -  6b + 4c +   d = -11
 3a +  9b - 6c +  5d =  10

    Since all 4 quadratics contain the term n(a + 3b) you can't solve for a or b - as long as c and d are consistant you should end up with an answer in the form of A + mB + const = 0 - ie. a straight line..

    eg: a + 3b = e

    so now solve these !
    just in case one of them is inconsistant - do it four times and leave out one equation each time - ie solve for c,d,e using any three equations. 
      e - 2c +  3d =   2
 4e - 8c + 14d =   6
-2e + 4c +   d = -11
 3e - 6c +  5d =  10


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