Mailing-List: contact dev-help@mahout.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@mahout.apache.org
Received-SPF: pass (athena.apache.org: domain of goksron@gmail.com designates
 209.85.216.42 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:date:message-id:subject:from:to
         :content-type:content-transfer-encoding;
        b=JmaXFL+/waSyM4ZSaZjsykjD3e30io3md5GK5bQfjfbYFkizUU8E/dBCD3Aa3YraWA
         xbx7kUNlVG91S85m07I0s1aWBiDhQ7K8RmhRDlSobWpiMWAWcrpFMLb0+nQZ3F3XO0vf
         hk9ZrNBovdxVz33AC6y3xNSC2XVwOTtM7OvWA=
MIME-Version: 1.0
In-Reply-To: <BANLkTikKwrBQp+h1J8CFmkTE_+90pEnTmg@mail.gmail.com>
References: 
 <888004344.23670.1304573943158.JavaMail.tomcat@hel.zones.apache.org>
	<672498739.32704.1305944747359.JavaMail.tomcat@hel.zones.apache.org>
	<BANLkTikKwrBQp+h1J8CFmkTE_+90pEnTmg@mail.gmail.com>
Date: Fri, 20 May 2011 21:14:35 -0700
Message-ID: <BANLkTikH3iOTT4BdczMgraKbJC7hq_eftA@mail.gmail.com>
Subject: Re: [jira] [Commented] (MAHOUT-687) Random generator objects- slight
 refactor
From: Lance Norskog <goksron@gmail.com>
To: dev@mahout.apache.org
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

Right! Ok. Yes, that makes a lot more sense. I'm parking my random
vector/matrix stuff because it's clear (to me at least) that
Vector&Matrix need some revamping.

But still, how should a random based on MurmurHash work?

Lance

On Fri, May 20, 2011 at 7:29 PM, Ted Dunning <ted.dunning@gmail.com> wrote:
> No. =C2=A0I was referring to the specific use of random number generators=
 to
> generate an ephemeral random matrix. =C2=A0I prefer to hash the element l=
ocation
> in order to generate the element value than to use a random number genera=
tor
> seeded by the element location. =C2=A0These are formally equivalent but
> practically quite different since hash functions are often designed with
> fast startup and PRNG's are often designed without much regard to startup=
 or
> reseeding cost. =C2=A0MersenneTwister in particular is a very bad generat=
or with
> respect to the cost of reseeding. =C2=A0Murmurhash is a very good example=
 of a
> lean hash function.
>
> On Fri, May 20, 2011 at 7:25 PM, Lance Norskog (JIRA) <jira@apache.org>wr=
ote:
>
>>
>> Ted, you mentioned wanting a MurmurHash Random class. Is this what you
>> envisioned? (It is not finished code; see below).
>>
>> {code}
>> public class MurmurHashRandom extends Random {
>> =C2=A0private long murmurSeed;
>> =C2=A0private final ByteBuffer buf;
>>
>> =C2=A0public MurmurHashRandom() {
>> =C2=A0 =C2=A0this(0);
>> =C2=A0}
>>
>> =C2=A0public MurmurHashRandom(int seed) {
>> =C2=A0 =C2=A0SeedGenerator gen =3D new FastRandomSeedGenerator();
>> =C2=A0 =C2=A0byte[] bits =3D RandomUtils.longSeedtoBytes(gen.generateSee=
d());
>> =C2=A0 =C2=A0buf =3D ByteBuffer.wrap(bits);
>> =C2=A0 =C2=A0this.murmurSeed =3D MurmurHash.hash64A(bits, seed);
>> =C2=A0}
>>
>> =C2=A0@Override
>> =C2=A0public long nextLong() {
>> =C2=A0 =C2=A0long oldSeed =3D murmurSeed;
>> =C2=A0 =C2=A0murmurSeed =3D MurmurHash.hash64A(buf, (int) murmurSeed);
>> =C2=A0 =C2=A0return oldSeed;
>> =C2=A0}
>>
>> {code}
>>
>>
>


--=20
Lance Norskog
goksron@gmail.com