While loops in Mathematica

  1. I am trying to do some Newton's method-type stuff in Mathematica.

    I want to build a While loop that does the following:

    - Take input r.
    - Compute some quantity f(r).
    - Update the value of r to f(r).

    - Repeat until |g(r)| < C for some fixed constant C.

    The third (boldfaced) step is the one I'm having trouble with. I don't know how to do this. Can someone help?
  2. jcsd
  3. Something like this?

    r=Input["What's r?"];(*Enter something between -1 and 1 *)

    If that doesn't give you enough then we need to see what you have already done
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