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There
is no "easy and good approximation" technique for cube roots. Here are
three methods to do what you want.
Using
system APIs, convert input argument to log(10), divide by 3, convert back.
Use
the power API function to raise the input argument to the 0.333...
power.
Write
an RPG program:
Assign
some value to a variable called tolerance.
Using
some technique that you invent, compute a seed value from input argument
and assign it to a variable named work.
TAG:
Cube variable work into a variable named cube.
Subtract the input value from cube and assign to a variable named
difference.
If the
absolute value of difference is greater than tolerance,
if difference is positive, adjust work
down
if difference is negative, adjust work
up
Go to tag
else
the current value of work is the cube root of input
argument
end
You
should be able to make this into a nice tight little loop, I wrote it in this
style because we don't have to have any arguments about syntax or
language. The RPG program is, in fact, the missing approximation technique
noted in the first sentence. You will note that it uses a technique called
successive approximation. It is good but not easy - it may require a lot
of CPU cycles in the cubing function to discover the answer.
Richard Jackson
(speaking only for myself)
-----Original Message-----
From: owner-rpg400-l@midrange.com [mailto:owner-rpg400-l@midrange.com]On Behalf Of Walter Hesius Sent: Wednesday, February 14, 2001 3:06 PM To: RPG400-L@midrange.com Subject: Cube root
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