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MathGroup Archive 2006

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RootSearch Performance

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72370] RootSearch Performance
  • From: "Ted Ersek" <ted.ersek at tqci.net>
  • Date: Tue, 26 Dec 2006 08:55:26 -0500 (EST)

About a week ago we had the thread:
   "FindRoot anomoly (example from Mathematica"
--------------------------------------------------------------
In that thread galordloo wrote:

Ersek's RootSearch function finds only seven roots to the equation
between x == 1 and x == 100:

sol == RootSearch[3*Cos[x] ==== Log[x], {x, 1, 100}]

      <snip>  (* Rules for seven roots, all between 1 and 20 were returned.=
 *)


---------------------------------
Then Carl Woll (of Wolfram Research) replied:

An alternative method is possible using IntervalBisection:
< snip > =20

The nice thing about IntervalBisection is that we were able to use an=20
initial range of {0,Infinity} instead of {1,100}. The other nice thing=20
about IntervalBisection is that we are guaranteed that all roots lie in=20
the interval given in the result, something that is not true with=20
RootSearch.

The price you pay is that the only transcendental functions allowed in=20
the input are trigonometric/exponential functions and their inverses,=20
i.e., only functions which support Interval arguments.

===========================================================================
======================
I wrote the RootSearch package, and it's designed to never look=20
for a root outside the range specified in the input. While=20
RootSearch has many lines of code, the ideas I use to limit the=20
range being searched are straight forward. I doubt you can find=20
an example where it returns a root outside the specified range.=20
However, if you can find an example that shows otherwise,=20
I would like to know about it.

         Ted Ersek
              Reply to:  Ted.Ersek at navy.mil


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