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Newtons method.

  1. Oct 28, 2008 #1
    when it asks to find the largest solution to 5 decimals, whats the initial value i start with for Xo and how many iterations should i do?

    thank you
  2. jcsd
  3. Oct 29, 2008 #2


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    Start with a reasonable guess, iterate until you reach the desired precision.

    Compare each iterate with the previous, when the difference is small enough you are done.
  4. Oct 30, 2008 #3
    One word of caution: Although Newtons method normally converges very fast, there is no guarantee that it will converge at all ! If you see the difference getting bigger instead of smaller (or some sort of oscillation), you know that Newton is running amok. Try to guess a new initial value and start again.

    If you have written a little program to do the job (and you should do so, doing this stuff manually is boring), the easiest solution to the non-convergence problem is to count the number of iterations. If you are not done after, say, 30 iterations, stop the program and ask the user for a new initial value.
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