1. Not finding help here? Sign up for a free 30min 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!

C3 coursework

  1. Jul 2, 2008 #1
    I am on my final part of my C3 coursework, doing the comparison of methods, i have found the root using the change of sign method, and the newton raphson method but i am struggling with using the rearranging method. the equation i am using is x^3 +5x -4, i have tried rearranging it to get the root which is 0.3274, but i can not get it to converge to this figure, the coursework is due in tomorrow at 4pm and i just need to do this final bit and i am done but i can't i have been tring for 3 hours please help me.

    Thanks

    I am not asking for it to be done for me i am just asking to know whati need to do to my equation to get my root 0.3274.
     
  2. jcsd
  3. Jul 3, 2008 #2
    Show me newton-raphson with your equation.
     
  4. Jul 3, 2008 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    I have no idea what you mean by the "rearranging method". Please explain.
     
  5. Jul 4, 2008 #4

    madmike159

    User Avatar
    Gold Member

    Hes talking about the g(x) method. You make your equation in the form x = ... then find points of interception on the graph y = x. These interceptions are the roots of the orignal equation.

    You need to find a root between 2 points using a integer search. Take the x value from the search and put it in to the x = equation. then take that value and put it in to the equation again untill it converges to 5/6 DP.

    eg x=x^3-2x/3
    x = (-1, 0)
    x0 = -1
    x1 = -1^3-2*-1/3 = n
    x2 = n^3-2*n/3 etc.
     
  6. Jul 4, 2008 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    What function are you talking about? x= x3- 2x/3 is equivalent to x3- (2/3)x- x= 0 or x3- (5/3)x= 0 which has NO roots between -1 and 0. The method you give will eventually converge to 0 which is a root.
     
  7. Jul 4, 2008 #6

    madmike159

    User Avatar
    Gold Member

    No I was giving an exampe of the steps you take. I didn't want to give him somthing that worked because it is course work, he can get marked down if some on did it for him. It works in the same way s the Newton Raphson method (gets a closer value every time) but isn' as quick.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: C3 coursework
Loading...