[erlang-questions] Integer square root

Kenji Rikitake <>
Tue Jan 26 02:54:36 CET 2010


My mistake. I didn't explore the operators "div" and "rem".
I confirmed those two operators worked.  Thanks Bob.
(So it's relatively easier now to do this...)

Kenji Rikitake

In the message <>
dated Mon, Jan 25, 2010 at 05:45:36PM -0800,
Bob Ippolito <> writes:
> On Mon, Jan 25, 2010 at 5:26 PM, Kenji Rikitake <> wrote:
> > Very long time ago I was trying to solve the square root
> > problem, but I didn't because handling in the float numbers
> > gave the sufficient precision for me.
> >
> > In general, a quick method of
> > solving X when Y = X * X and Y is given (X, Y are bignums) as:
> >
> > 1) Obtain approximation of X by float sqrt of Y
> > ?? separately to significand and exponent
> > ?? (note: IEEE754 format has its own limits in
> > ?? ?? ?? ?? ??the digits of exponent too)
> >
> > 2) applying Newton-Raphson method so that
> > ?? Xnew = (X + (Y / X)) / 2
> >
> > 3) Repeat finding Xnew on 2) until Xnew =:= X
> >
> > Things you need to invent:
> >
> > * bignum integer dividing program
> > ??(bignum / bignum -> bignum (+ remainder, maybe))
> > ??(This is NOT provided by Erlang)
> 
> Sure it is, div and rem work with bignums. Not sure about how
> efficient it is relative to other bignum implementations but it works.
> 
> -bob


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