| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors; Free Springer Books; Books on Religion; Books on Linguistics; Palestinan Electronica; Books In Anthropology; Taylor Expansions of Spacetime; Info on Juniper; Efficient Stream Processing; The Moral Character of Crypto; Hearing Aid Info; Small Success With Go!; Re: Quick message - This link is broken; Adding Reverb To The Echo Chamber; Sox Audio Tools

© 2006-2015 Andrew Cooke (site) / post authors (content).

Efficient Entropy Estimates for Sequences of Large Values with OpenCL

From: andrew cooke <andrew@...>

Date: Sat, 8 Oct 2011 21:43:34 -0300

I need to estimate the entropy of sequences of large numbers in OpenCL.

The basic idea is to find how often each number occurs and then use the
Shannon (p ln(p)) formula.  But doing that naively in OpenCL is hard - the
numbers are too large to use a simple array (where we increment array[n] each
time we find value n).

(By "large number" I mean that they are represented as an arbitrary number of
32 bit ints).

The sequence length is much shorter than the maximum number and although the
numbers are large certain values are likely to repeat often.  So one approach
is to generate a lookup-table that associates each number with an index and
then historgam the indices.  But I cannot see how to do that efficiently or
easily in OpenCL.

The best idea I have had so far is to use modular arithmetic.  For example,
take the numbers modulo 2^8 and then increment a 255 entry array.  But modulo
2^n simply discards bits past n and the numbers are actually "bit patterns",
so I don't want to do that.  So it seems better to work modul some prime value
(or perhaps several).

Thanks to the magic of modular arithmetic it seems to be relatively easy to
convert large (multi-int32) numbers to their modulo:

   a0 + 2^32 (a1 + 2^32 (a2 + ...))
     = (a0 % n) + (2^32 % n) * ((a1 % n) + (2^32 % n) * ((a2 % n) + ...))

and if I use a prime less than 2^16 (I am thinking a value like 17 might be
enough!) then I can do the above in 32 bit ints without any problems.

I hope that makes sense.  Anyone have any better ideas?  I don't need entropy
exactly - all I want is a number that indicates "how statistically random"
some sequence is in a way that is reasonably smooth and sensitive (since it
will be used as a fitness measure in a GA).  And no, I don't really have any
clues about what a good statistical measure would be, but it would be nice if
it could reject a simple counter (which entropy cannot, so there is certainly
room for improvement).

(Background - the values are the binary state of a system that generates
"rhythms"; the system is deterministic it and tends "naturally" to generate
simple repeating patterns - the aim is to evolve away from that).

Andrew

Radix Sorting

From: andrew cooke <andrew@...>

Date: Sat, 8 Oct 2011 22:22:44 -0300

I just remembered - radix sorting is probably the "right" way to do this.

See for example http://www.moderngpu.com/sort/algo.html

Andrew

Comment on this post