Author Archive for peter

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By their voice ye shall know them

Published by peter on 2010-07-28 in Computer Science, Computer technology and Computing-as-interaction. 0 Comments

Effective strategies are often counter-intuitive.  If you are speaking to a large group, some of whom are speaking to each other, your natural tendency will be to try to speak over them, to speak more loudly.  But doing this just encourages the talkers in the audience to increase their levels of speech, and so an arms race results.   Better for you to speak more softly, which means that audience talkers can hear themselves more clearly over you, and so typically, and unthinkingly, drop the levels of their own speech.
A recent issue of ACM Transactions on Computer Systems (ACM TOCS) carries a paper with a wonderful example of this principle.  Faced with a denial-of-service attack, they propose that a server ask all its clients to increase their messages to the server.  Most likely, attackers among the clients are already transmitting at their local full capacity, and so are unable to do this, which means that messages from attackers will form a decreasing proportion of all messages received by the server.   The paper abstract is:

This article presents the design, implementation, analysis, and experimental evaluation of speak-up, a defense against application-level distributed denial-of-service (DDoS), in which attackers cripple a server by sending legitimate-looking requests that consume computational resources (e.g., CPU cycles, disk). With speak-up, a victimized server encourages all clients, resources permitting, to automatically send higher volumes of traffic. We suppose that attackers are already using most of their upload bandwidth so cannot react to the encouragement. Good clients, however, have spare upload bandwidth so can react to the encouragement with drastically higher volumes of traffic. The intended outcome of this traffic inflation is that the good clients crowd out the bad ones, thereby capturing a much larger fraction of the server’s resources than before. We experiment under various conditions and find that speak-up causes the server to spend resources on a group of clients in rough proportion to their aggregate upload bandwidths, which is the intended result.

Reference:
Michael Walfish, Mythili Vukurutu, Hari Balakrishnan, David Karger and Scott Shenker [2010]:  DDoS defense by offense.  ACM Transactions on Computer Systems, 28 (1), article 3.

Berger on drawing

Published by peter on 2010-07-28 in Art, Creativity, Design, Hands and Human intelligence. 0 Comments

Following Bridget Riley on drawing-as-thinking, I have been reading Jim Savage’s fascinating collection of writings by John Berger on the topic of drawing.  Although Berger does not say so, he is talking primarily about representational drawing – the drawing of things in the world (whether seen or remembered) or things in some imagined world – not abstract drawing.  Some excerpts:

  • “For the artist drawing is discovery.  And that is not just a slick phrase, it is quite literally true.  It is the actual act of drawing that forces the artist to look at the object in front of him, to dissect it in his mind’s eye and put it together again; or, if he is drawing from memory, that forces him to dredge his own mind, to discover the content of his own store of past observations.” (page 3)
  • “It is a platitude in the teaching of drawing that the heart of the matter lies in the specific process of looking.  A line, an area of tone, is not really important because it records what you have seen, but because of what it will lead you on to see.  Following up its logic in order to check its accuracy, you find confirmation or denial in the object itself or in your memory of it.  Each confirmation or denial brings you closer to the object, until finally you are, as it were, inside it:  the contours you have drawn no longer marking the edge of what you have seen, but the edge of what you have become.  Perhaps that sounds needlessly metaphysical.  Another way of putting it would be to say that each mark you make on the paper is a stepping-stone from which you proceed to the next, until you have crossed your subject as though it were a river, have put it behind you.” (page 3)
  • “A drawing is an autobiographical record of one’s discovery of an event – seen, remembered or imagined.” (page 3)
  • “A drawing of a tree shows, not a tree, but a tree-being-looked-at.  . . .  Within the instant of the sight of a tree is established a life-experience.” (page 71)
  • “All genuine art approaches something which is eloquent but which we cannot altogether understand.  Eloquent because it touches something fundamental.  How do we know?  We do not know.  We simply recognize.”   (page 80)
  • “Art cannot be used to explain the mysterious.  What art does is to make it easier to notice. Art uncovers the mysterious. And when noticed and uncovered, it becomes more mysterious.”  (page 80)
  • “The pen with which I’m writing is the one with which I draw.  And there are times, like tonight, when it won’t flow and when it demands a bath or a hand moving differently.  All drawings are a collaboration, like most circus-acts.” (page 110)
  • “where are we, during the act of drawing, in spirit?  Where are you at such moments – moments which add up to so many, one might think of them as another life-time?    Each pictorial tradition offers a different answer to this query.  For instance, the European tradition, since the Renaissance, places the model over there, the draughtsman here, and the paper somewhere in between, within arms reach of the draughtsman, who observes the model and notes down what he has observed on the paper in front of him.   The Chinese tradition arranges things differently.  Calligraphy, the trace of things, is behind the model and the draughtsman has to search for it, looking through the model.   On his paper he then repeats the gestures he has seen calligraphically.  For the Paleolithic shaman, drawing inside a cave, it was different again.  The model and the drawing surface were in the same place, calling to the draughtsman to come and meet them, and then trace, with his hand on the rock, their presence.” (page 123)

Reference:
John Berger [2005]:  Berger on Drawing.  Edited by Jim Savage.  Aghabullogue, Co. Cork, Eire:  Occasional Press.  Second Edition, 2007.
I have written more on the relationships between hand and mind and eye and object here.

Concat 2: Art criticism

Published by peter on 2010-07-25 in Art and Concats. Closed

Here a concatenation of various recent articles on art which have interested me, and a reproduction of International Klein Blue, Yves Klein’s patented colour.

Poem: Out of the Cradle Endlessly Rocking

Published by peter on 2010-07-25 in Poetry. Closed

An excerpt from Walt Whitman’s superb Sea-Drift, written in 1859, about alone-ness and becoming a poet.

Out of the Cradle Endlessly Rocking

Out of the cradle endlessly rocking,
Out of the mocking-bird’s throat, the musical shuttle,
Out of the Ninth-month midnight,
Over the sterile sands and the fields beyond, where the child
leaving his bed wander’d alone, bareheaded, barefoot,
Down from the shower’d halo,
Up from the mystic play of shadows twining and twisting as if they
were alive,
Out from the patches of briers and blackberries,
From the memories of the bird that chanted to me,
From your memories sad brother, from the fitful risings and fallings I heard,
From under that yellow half-moon late-risen and swollen as if with tears,
From those beginning notes of yearning and love there in the mist,
From the thousand responses of my heart never to cease,
From the myriad thence-arous’d words,
From the word stronger and more delicious than any,
From such as now they start the scene revisiting,
As a flock, twittering, rising, or overhead passing,
Borne hither, ere all eludes me, hurriedly,
A man, yet by these tears a little boy again,
Throwing myself on the sand, confronting the waves,
I, chanter of pains and joys, uniter of here and hereafter,
Taking all hints to use them, but swiftly leaping beyond them,
A reminiscence sing.

Once Paumanok,
When the lilac-scent was in the air and Fifth-month grass was growing,
Up this seashore in some briers,
Two feather’d guests from Alabama, two together,
And their nest, and four light-green eggs spotted with brown,
And every day the he-bird to and fro near at hand,
And every day the she-bird crouch’d on her nest, silent, with bright eyes,
And every day I, a curious boy, never too close, never disturbing
them,
Cautiously peering, absorbing, translating.
Shine! shine! shine!
Pour down your warmth, great sun.’
While we bask, we two together.
Two together!
Winds blow south, or winds blow north,
Day come white, or night come black,
Home, or rivers and mountains from home,
Singing all time, minding no time,
While we two keep together.
Till of a sudden,
May-be kill’d, unknown to her mate,
One forenoon the she-bird crouch’d not on the nest,
Nor return’d that afternoon, nor the next,
Nor ever appear’d again.
And thenceforward all summer in the sound of the sea,
And at night under the full of the moon in calmer weather,
Over the hoarse surging of the sea,
Or flitting from brier to brier by day,
I saw, I heard at intervals the remaining one, the he-bird,
The solitary guest from Alabama.
Blow! blow! blow!
Blow up sea-winds along Paumanok’s shore;
I wait and I wait till you blow my mate to me.
. . .

Previous poems are here.
Reference:
Walt Whitman [1982]:  Complete Poetry and Collected Prose.  Selected by Justin Kaplan. New York, NY, USA:  The Library of America.

Strategy vs. Tactics

Published by peter on 2010-07-23 in Decision theory, Game theory, History, Intelligence and Espionage and Military strategy. Closed

What is the difference between strategy and tactics?  In my experience, many people cannot tell the difference, and/or speak as if they conflate the two. Personally, I have never had difficulty telling them apart.
The 18th-century British naval definition was that tactics are for when you can see the enemy’s ships, and strategies are for when you cannot.  When you can see the enemy’s ships there are still important unknown variables, but you should know how many ships there are, where they are located, and (within some degree of accuracy) what hostile actions they are capable of.  If you are close enough to identify the particular enemy ships that you can see, you may also know then the identities of their captains.  With knowledge of past engagements, you may thus be able to estimate the intentions, the likely behaviors, and the fighting will of the ships’ crews.   None of these variables are known when the ships lay beyond the horizon.
Thus, tactics describe your possible actions when you know who the other stakeholders are in the situation you are in, and you have accurate (although not necessarily precise) information about their capabilities, goals, preferences, and intentions.   To the extent that such knowledge is missing is the extent to which reasoning about potential actions becomes strategic rather than tactical.  These distinctions are usually quite clear in marketing contexts.  For instance, licking envelopes for a client’s direct marketing campaign is not strategic consultancy, nor is finding, cleaning, verifying, and compiling the addresses needed by the client to put on the envelopes. (This is not to say that either task can be done well without expertise and experience.) Advising a client to embark on a direct marketing campaign rather than (say) a television ad campaign is closer to strategic consultancy, although in some contexts it may be mere tactics. Determining ahead of time which segments of the potential customer population should be targeted with an advertising campaign is definitely strategic, as is deciding whether or not to enter (or stay) in the market.
The key difference between the two is that articulating a strategy requires taking a view on the values of significant uncertain variables, whereas articulating a tactic generally does not.

Writing Shakespeare

Published by peter on 2010-07-22 in Books, Culture, Fiction, History, Literature, Poetry and Shakespeare. 0 Comments

Since the verified facts of Shakespeare’s life are so few, even a person normally skeptical of conspiracy theories could well consider it possible that the plays and poetry bearing the name of William Shakespeare were written by A. N. Other. But just who could have been that other?
Well, even with few verified facts about Shakespeare’s life, we can know some facts about the author of these texts by reading the texts themselves.  Whoever was the author must have spent a lot of time hanging about with actors, since knowledge of, and in-jokes about, acting and the theatre permeate the plays.  Also, whoever it was must have grown up in a rural district, not in a big city, since the author of the plays and the poetry knows a great deal about animals and plants, about rural life and its myths and customs, and rural pursuits.  Whoever it was also had close connections to Warwickshire, since the plays contain words specific to that area.
Also, whoever it was must have had close personal or family connections to the old religion (Catholicism), since many of the plays make detailed reference to, or indeed seem to be allegories of, the religious differences of the time (Wilson 2004, Asquith 2005). Whoever it was was close enough to the English court to write plays which discussed current political issues using historically-relevant allegories, yet not so close that these plays themselves or their performances (with just one exception) were seen as interventions in court intrigues.
Whoever it was also knew well the samizdat poetry of Robert Southwell, poet and Jesuit martyr, since some of the poetry and plays respond directly to Southwell’s poetry and prose (Wilson 2004, Klause 2008). To have responded to Southwell’s writing before 1595, as the writer of Shakespeare’s narrative poems and early plays did, required access to Southwell’s unpublished, illegal, dissident manuscripts.  Southwell and Shakespeare were cousins (Klause 2008 has a family tree).
And finally whoever it was was not a playwright or poet already known to us, since these texts differ stylistically from all other written work of the period, while exhibiting strong stylistic similarity among themselves.
There is only one candidate who fits all these criteria, and his name is William Shakespeare. Anyone seriously proposing an alternative to Shakespeare as the author of Shakespeare’s plays and poetry needs to explain how that person could have written poetry and plays with all the features described above. Every alternative theory so far advanced – Kit Marlowe, the Earl of Oxford, Francis Bacon, Elizabeth I, et al. – falls at the factual hurdles created by the texts themselves.
Note: Klause [2008, p. 40] presents a genealogy which shows that Robert Southwell and William Shakespeare shared a great-great-great-great-great-grandfather, Sir Robert Belknap (c. 1330-1401, Chief Justice of the Court of Common Pleas of England, 1377-1388) – Southwell through his mother, Bridget Copley, and Shakespeare through his mother, Mary Arden.  In addition, the great-great-grandfather, Sir John Gage, of Shakespeare’s patron, Henry Wriothesley, Third Earl of Southampton, was also grandfather to Edward Gage, husband of Margaret Shelley, Southwell’s mother’s first cousin and, like his mother, a descendant of Sir Robert Belknap.  In the extended families of Elizabethan society, all three – Shakespeare, Southwell and Wriothesley – would have been seen as, and would have known each other as, cousins.   The bonds across such extended family relationships were strong.   Having lived in contemporary societies (in Southern Africa) where extended families still play a prominent role (Bourdillon 1976), the strong loyalty and close brotherhood engendered across such apparently-distant connections is perfectly understandable to me, if not yet to all Shakespeare scholars.
References:
Clare Asquith [2005]: Shadowplay: The Hidden Beliefs and Coded Politics of William Shakespeare.  UK: Public Affairs.
Michael F. Bourdillon [1976]: The Shona Peoples: An Ethnography of the Contemporary Shona, with Special Reference to their Religion. Shona Heritage Series. Gwelo, Rhodesia (now Gweru, Zimbabwe):  Mambo Press.
John Klause [2008]:  Shakespeare, the Earl and the Jesuit.  Madison, NJ, USA: Fairleigh Dickinson University Press.
Anne R. Sweeney [2006]: Robert Southwell: Snow in Arcadia:  Redrawing the English Lyric Landscape 1586-1595. Manchester, UK:  Manchester University Press.
Richard Wilson [2004]: Secret Shakespeare:  Studies in Theatre, Religion and Resistance. Manchester, UK:  Manchester University Press.

Concat 1: The GEC

Published by peter on 2010-07-21 in Concats, Economics, Global Economic Crisis, History and Politics. Closed

A post to concatenate interesting material on the GFC and the GEC:

Informatics

Published by peter on 2010-07-16 in Computer Science and Computer technology. Closed

A recent issue of the Communications of the ACM has an interesting article about degrees in Informatics, by Dennis Groth and Jeffrey Mackie-Mason.  They present a nice definition of the subject in this para:

The vision for informatics follows from the natural evolution of computing. The success of computing is in the resolution of problems, found in areas that are predominately outside of computing. Advances in computing—and computing education—require greater understanding of the problems where they are found: in business, science, and the arts and humanities. Students must still learn computing, but they must learn it in contextualized ways. This, then, provides a definition for informatics: informatics is a discipline that solves problems through the application of computing or computation, in the context of the domain of the problem. Broadening computer science through attention to informatics not only offers insights that will drive advances in computing, but also more options and areas of inquiry for students, which will draw increasing numbers of them to study computation.

Sadly, these views are not uncontroversial, as the online experiences which motivated my parody here illustrate.  The interesting experience of Georgia Tech, where the School of Computing is split into three parts  — Computer Science; Interactive Computing; and Computational Science and Engineering, — is described here.
Reference:
Dennis P. Groth and Jeffrey K. MacKie-Mason [2010]: Why an Informatics degree?  Isn’t computer science enough? Communications of the ACM, 53 (2):  26-28.  Available here.

At Swim-two-birds

Published by peter on 2010-07-10 in Art, Creativity, Music, Prophecy and Uncertainty. Closed


Brian Dillon reviews a British touring exhibition of the art of John Cage, currently at the Baltic Mill Gateshead.
Two quibbles:  First, someone who compare’s Cage’s 4′ 33” to a blank gallery wall hasn’t actually listened to the piece.  If Dillon had compared it to a glass window in the gallery wall allowing a view of the outside of the gallery, then he would have made some sense.  But Cage’s composition is not about silence, or even pure sound, for either of which a blank gallery wall might be an appropriate visual representation.  The composition is about ambient sound, and about what sounds count as music in our culture.
Second, Dillon rightly mentions that the procedures used by Cage for musical composition from 1950 onwards (and later for poetry and visual art) were based on the Taoist I Ching.  But he wrongly describes these procedures as being based on “the philosophy of chance.”     Although widespread, this view is nonsense, accurate neither as to what Cage was doing, nor even as to what he may have thought he was doing.   Anyone subscribing to the Taoist philosophy underlying them understands the I Ching procedures as examplifying and manifesting hidden causal mechanisms, not chance.   The point of the underlying philosophy is that the random-looking events that result from the procedures express something unique, time-dependent, and personal to the specific person invoking the I Ching at the particular time they invoke it. So, to a Taoist, the resulting music or art is not “chance” or “random” or “aleatoric” at all, but profoundly deterministic, being the necessary consequential expression of deep, synchronistic, spiritual forces. I don’t know if Cage was himself a Taoist (I’m not sure that anyone does), but to an adherent of Taoist philosophy Cage’s own beliefs or attitudes are irrelevant to the workings of these forces.  I sense that Cage had sufficient understanding of Taoist and Zen ideas (Zen being the Japanese version of Taoism) to recognize this particular feature:  that to an adherent of the philosophy the beliefs of the invoker of the procedures are irrelevant.
In my experience, the idea that the I Ching is a deterministic process is a hard one for many modern westerners to understand, let alone to accept, so entrenched is the prevailing western view that the material realm is all there is.  This entrenched view is only historically recent in the west:  Isaac Newton, for example, was a believer in the existence of cosmic spiritual forces, and thought he had found the laws which governed their operation.    Obversely, many easterners in my experience have difficulty with notions of uncertainty and chance; if all events are subject to hidden causal forces, the concepts of randomness and of alternative possible futures make no sense.  My experience here includes making presentations and leading discussions on scenario analyses with senior managers of Asian multinationals.
We are two birds swimming, each circling the pond, warily, neither understanding the other, neither flying away.
References:
Kyle Gann [2010]: No Such Thing as Silence.  John Cage’s 4′ 33”.  New Haven, CT, USA:  Yale University Press.
James Pritchett [1993]:  The Music of John Cage.  Cambridge, UK:  Cambridge University Press.

Bayesian statistics

Published by peter on 2010-07-08 in AI, Decision theory, Mathematics and Uncertainty. Closed

One of the mysteries to anyone trained in the frequentist hypothesis-testing paradigm of statistics, as I was, and still adhering to it, as I do, is how Bayesian approaches seemed to have taken the academy by storm.   One wonders, first, how a theory based – and based explicitly – on a measure of uncertainty defined in terms of subjective personal beliefs, could be considered even for a moment for an inter-subjective (ie, social) activity such as Science.

One wonders, second, how a theory justified by appeals to such socially-constructed, culturally-specific, and readily-contestable activities as gambling (ie, so-called Dutch-book arguments) could be taken seriously as the basis for an activity (Science) aiming for, and claiming to achieve, universal validity.   One wonders, third, how the fact that such justifications, even if gambling presents no moral, philosophical or other qualms,  require infinite sequences of gambles is not a little troubling for all of us living in this finite world.  (You tell me you are certain to beat me if we play an infinite sequence of gambles? Then, let me tell you, that I have a religion promising eternal life that may interest you in turn.)

One wonders, fourthly, where are recorded all the prior distributions of beliefs which this theory requires investigators to articulate before doing research.  Surely someone must be writing them down, so that we consumers of science can know that our researchers are honest, and hold them to potential account.   That there is such a disconnect between what Bayesian theorists say researchers do and what those researchers demonstrably do should trouble anyone contemplating a choice of statistical paradigms, surely. Finally, one wonders how a theory that requires non-zero probabilities be allocated to models of which the investigators have not yet heard or even which no one has yet articulated, for those models to be tested, passes muster at the statistical methodology corral.

To my mind, Bayesianism is a theory from some other world – infinite gambles, imagined prior distributions, models that disregard time or requirements for constructability,  unrealistic abstractions from actual scientific practice – not from our own.

So, how could the Bayesians make as much headway as they have these last six decades? Perhaps it is due to an inherent pragmatism of statisticians – using whatever techniques work, without much regard as to their underlying philosophy or incoherence therein.  Or perhaps the battle between the two schools of thought has simply been asymmetric:  the Bayesians being more determined to prevail (in my personal experience, to the point of cultism and personal vitriol) than the adherents of frequentism.  Greg Wilson’s 2001 PhD thesis explored this question, although without finding definitive answers.

Now, Andrew Gelman and the indefatigable Cosma Shalizi have written a superb paper, entitled “Philosophy and the practice of Bayesian statistics”.  Their paper presents another possible reason for the rise of Bayesian methods:  that Bayesianism, when used in actual practice, is most often a form of hypothesis-testing, and thus not as untethered to reality as the pure theory would suggest.  Their abstract:

A substantial school in the philosophy of science identifies Bayesian inference with inductive inference and even rationality as such, and seems to be strengthened by the rise and practical success of Bayesian statistics. We argue that the most successful forms of Bayesian statistics do not actually support that particular philosophy but rather accord much better with sophisticated forms of hypothetico-deductivism.  We examine the actual role played by prior distributions in Bayesian models, and the crucial aspects of model checking and model revision, which fall outside the scope of Bayesian confirmation theory. We draw on the literature on the consistency of Bayesian updating and also on our experience of applied work in social science.

Clarity about these matters should benefit not just philosophy of science, but also statistical practice. At best, the inductivist view has encouraged researchers to fit and compare models without checking them; at worst, theorists have actively discouraged practitioners from performing model checking because it does not fit into their framework.

References:
Andrew Gelman and Cosma Rohilla Shalizi [2010]:  Philosophy and the practice of Bayesian statistics.  Available from Arxiv.  Blog post here.

Gregory D. Wilson [2001]:   Articulation Theory and Disciplinary Change:  Unpacking the Bayesian-Frequentist Paradigm Conflict in Statistical Science.  PhD Thesis,  Rhetoric and Professional Communication Programme, New Mexico State University.  Las Cruces, NM, USA.  July 2001.