Re: count zeros in a number
- To: mathgroup at smc.vnet.net
- Subject: [mg121862] Re: count zeros in a number
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Wed, 5 Oct 2011 04:01:39 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <201110020636.CAA28027@smc.vnet.net> <j6brvm$8om$1@smc.vnet.net>
- Reply-to: drmajorbob at yahoo.com
A person just introduced to Mathematica is NOT, as yet, a Mathematica
programmer.
Bobby
On Tue, 04 Oct 2011 15:57:30 -0500, Richard Fateman
<fateman at eecs.berkeley.edu> wrote:
> On 10/4/2011 9:44 AM, DrMajorBob wrote:
>> There's nothing "esoteric" about IntegerDigits, Replace, or Repeated,
>> as in:
>>
>> x = 24^24*55^55;
>> Replace[IntegerDigits@x, {__, zeroes : 0 ..} :>
>> Length@{zeroes}] // Timing
>>
>> {0.000185, 55}
>
> My feeling is that these ARE esoteric. A person just introduced to
> Mathematica would probably not encounter IntegerDigits, Repeated, or
> patterns other than the trivial one used in pseudo function definitions
> as
> f[x_]:= x+1.
>
>
>>
>> If we wanted brute-force arithmetic, we might use Fortran.
>>
>> Your suggested solutions are NOT greatly hindered by "the slow
>> implementation of looping constructs in Mathematica", on the other hand:
>>
>> (n = 0; While[GCD[x, 10^n] == 10^n, n++]; n - 1) // Timing
>>
>> {0.000029, 0}
>
> huh? I got {0., 55}. Perhaps my computer is faster or has a lower
> resolution timer, but we should both get 55.
>
>>
>> (n = 0; While[Mod[x, 10] == 0, (x = x/10; n++)]; n) // Timing
>>
>> {0.000018, 0}
>
> I mention the slow implementation of looping constructs simply to warn
> people that if you can resolve your computation by simple composition of
> built-in functions e.g. F[G[H[x]]] and don't rely on Mathematica
> to efficiently execute loops written as While[] For[] etc, you are
> probably going to run faster. Let Mathematica's operation on compound
> objects like lists do the job. Length[] is a lot faster than counting
> with a While etc.
>
> In my timings, doing the operations 1000 times..
> Do[.....,{1000}]//Timing
>
> I found that my solutions were about 10X faster than the IntegerDigits
> one, on this particular value of x.
>
> Fortran can't be used unless you manage arbitrary precision integers...
>
> RJF
>
>
>
--
DrMajorBob at yahoo.com
- References:
- count zeros in a number
- From: dimitris <dimmechan@yahoo.com>
- count zeros in a number