Colliding balls approximate pi
Found via G+, a new physical experiment that approximates , like Buffon’s needle problem: The Pi Machine.
Roughly, the amazing discovery of Gregory Galperin is this: When a ball of mass collides with one of ball , propelling it towards a wall, the number of collisions (assuming standard physics idealisms) is , so by taking , we can get the first digits of . Note that this number of collisions is an entirely determinstic quantity; there’s no probability is involved!
Here’s a video demonstrating the fact for (the blue ball is the heavier one):
The NYT post says how this discovery came about:
Dr. Galperin’s approach was also geometric but very different (using an unfolding geodesic), building on prior related insights. Dr. Galperin, who studied under well-known Russian mathematician Andrei Kolmogorov, had recently written (with Yakov Sinai) extensively on ball collisions, realized just before a talk in 1995 that a plot of the ball positions of a pair of colliding balls could be used to determine pi. (When he mentioned this insight in the talk, no one in the audience believed him.) This finding was ultimately published as “Playing Pool With Pi” in a 2003 issue of Regular and Chaotic Dynamics.
The paper, Playing Pool With π (The number π from a billiard point of view) is very readable. The post has, despite a “solution” section, essentially no explanation, but the two comments by Dave in the comments section explain it clearly. And a reader sent in a cleaned-up version of that too: here, by Benjamin Wearn who teaches physics at Fieldston School.
Now someone needs to make a simulation / animation graphing the two balls in phase space of momentum. :-)
I’d done something a while ago, to illustrate The Orbit of the Moon around the Sun is Convex!, here. Probably need to re-learn all that JavaScript stuff, to make one for this. Leaving this post here as a placeholder.
Or maybe someone has done it already?
The Indian theory of aesthetic appreciation (rasa)
Here’s a great, simple write-up aimed at a Western audience, from the Clay Sanskrit Library edition of Kālidāsa’s The Recognition of Shakuntala, written by Somadeva Vasudeva:
Imagine that you find yourself going to see a performance of “Romeo and Juliet.” You are in the right mood for the play, no mundane worries preoccupy your mind, you have agreeable company, and the theatre, the stage, the director and the actors are all excellent—capable of doing justice to a great play. Your seat in the theatre is comfortable and gives an unobstructed view.
The play begins and you find yourself drawn into the world Shakespeare is sketching. The involvement deepens to an immersion where the ordinary, everyday world dims and fades from the center of attention, you begin to understand and even share the feelings of the characters on stage—under ideal conditions you might reach a stage where you
begin to participate in some strange way in the love being evoked.Now, if at that moment you were to ask yourself: “Whose love is this?” a paradox arises.
It cannot be Romeo’s love for Juliet, nor Juliet’s love for Romeo, for they are fictional characters. It cannot be the actors’, for in reality they may despise one another. It cannot be your own love, for you cannot love a fictional character and know nothing about the actors’ real personalities (they are veiled by the role they assume), and, for the same reasons, it cannot be the actors’ love for either you or the fictional characters. So it is a peculiar, almost abstract love without immediate referent or context.
A Sanskrit aesthete would explain to you that you are at that moment “relishing” (āsvādana) your own “fundamental emotional state” (sthāyi-bhāva) called “passion” (rati) which has been “decontextualised” (sādhāraṇīkṛta) by the operation of “sympathetic resonance” (hṛdayasaṃvāda) and heightened to become transformed into an “aesthetic sentiment” (rasa) called the “erotic sentiment” (śṛṅgāra).
This “aesthetic sentiment” is a paradoxical and ephemeral thing that can be evoked by the play but is not exactly caused by it, for many spectators may have felt nothing at all during the same performance. You yourself, seeing it again next week, under the same circumstances, might experience nothing. It is, moreover, something that cannot be adequately explained through analytic terms, the only proof for its existence is its direct, personal experience.
[…]
It is, moreover, a blissful experience. The fact that sensitive readers often weep while reading poetry does not mean that they are suffering, rather the tenderness of the work has succeeded in melting the contraction of their minds or hearts.
The non-ordinary nature of such aesthetic sentiments makes it possible for the spectator or reader to derive a pleasurable experience even from what in ordinary life would be causes of grief.
The Indian scholarly tradition has a lot more, including some very thoughtful deliberation and perceptive observation, but it seems good to start a discussion of rasa with an example like this, than to start with the technical details.
[Another good start may be via film. See for instance:
How to Watch a Hindi Film: The Example of Kuch Kuch Hota Hai by Sam Joshi, published in Education About Asia, Volume 9, Number 1 (Spring 2004).
and perhaps (and if you have a lot of time):
Is There an Indian Way of Filmmaking? by Philip Lutgendorf, published in International Journal of Hindu Studies, Vol. 10, No. 3 (Dec., 2006), pp. 227-256.
Previously on this blog: On songs in Bollywood]
The rest is commentary
Famous verses appear in many variants. Thanks to Google, it is easy to find many of them. For “paropakāraḥ puṇyāya, pāpāya parapīḍanam”, Google throws up a lot of variants for the first half.
The Vikramacarita has:
śrūyatāṃ dharmasarvasvaṃ, yad uktaṃ śāstrakoṭibhiḥ /
paropakāraḥ puṇyāya, pāpāya parapīḍanam
Other variants are:
saṅkṣepāt kathyate dharmo janāḥ kiṃ vistareṇa vaḥ |
paropakāraḥ puṇyāya pāpāya para-pīḍanam ||Panc_3.103||
or
aṣṭādaśapurāṇeṣu vyāsasya vacanadvayam /
paropakāraḥ puṇyāya pāpāya parapīḍanam //
or
ślokārdhena pravakṣyāmi yaduktaṃ grantha-koṭibhiḥ
paropakāraḥ puṇyāya pāpāya parapīḍanam
Going by the first line gives other verses:
śrūyatāṃ dharmasarvasvaṃ śrutvā caivāvadhāryatām | (or caiva vicāryatām ।)
ātmanaḥ pratikūlāni pareṣāṃ na samācaret ||
[Cāṇakya-nīti, Pañcatantra, Subhāṣitāvalī etc.]
See also:
https://en.wikipedia.org/wiki/Golden_Rule
prāṇā yathātmano ‘bhīṣṭā bhūtānām api te tathā |
ātmaupamyena gantavyaṃ buddhimadbhir mahātmabhiḥ
तस्माद्धर्मप्रधानेन भवितव्यं यतात्मना ।
तथा च सर्वभूतेषु वर्तितव्यं यथात्मनि ॥ Mahābhārata Shānti-Parva 167:9
(http://blog.practicalsanskrit.com/2013/05/do-unto-others-golden-rule-of-humanity.html)
05,039.057a na tatparasya saṃdadhyāt pratikūlaṃ yadātmanaḥ
05,039.057b*0238_01 ātmanaḥ pratikūlāni vijānan na samācaret
05,039.057c saṃgraheṇaiṣa dharmaḥ syāt kāmād anyaḥ pravartate
As Hillel says, the rest is commentary.
For (some) commentary, go here.
Prefatory apprehension
Robert Recorde’s 1557 book is noted for being the first to introduce the equals sign =, and is titled:
The Whetstone of Witte: whiche is the seconde parte of Arithmeteke: containing the extraction of rootes; the cossike practise, with the rule of equation; and the workes of Surde Nombers.
Its title page (see http://www.maa.org/publications/periodicals/convergence/mathematical-treasures-robert-recordes-whetstone-of-witte, see also the full book at https://archive.org/stream/TheWhetstoneOfWitte#page/n0/mode/2up) contains this verse:
Original spelling
Though many ſtones doe beare greate price, The grounde of artes did brede this ſtone: |
Modern spelling
Though many stones do bear great price, The ground of arts did breed this stone; |
Apparently the full title contains a pun (see http://www.pballew.net/arithm17.html): “the cossike practise” in the title refers to algebra, as the Latin cosa apparently meaning “a thing” was used to stand for an unknown, abbreviated to cos — but the Latin word cos itself means a grindstone.
The author again reminds readers not to blame his book, at the end of his preface:
To the curiouſe ſcanner.
If you ought finde, as ſome men maie, But if you mende not that you blame, |
Authors are either anxious about how their book is received, or make sure to be pointedly uncaring.
Sir Arthur Conan Doyle, in a mostly forgettable volume of poetry (Songs of the Road, 1911), begins:
If it were not for the hillocks
You’d think little of the hills;
The rivers would seem tiny
If it were not for the rills.
If you never saw the brushwood
You would under-rate the trees;
And so you see the purpose
Of such little rhymes as these.
Kālidāsa of course begins his Raghuvaṃśa with a grand disclaimer:
kva sūryaprabhavo vaṃśaḥ kva cālpaviṣayā matiḥ /
titīrṣur dustaram mohād uḍupenāsmi sāgaram // Ragh_1.2 //mandaḥ kaviyaśaḥ prārthī gamiṣyāmy upahāsyatām /
prāṃśulabhye phale lobhād udbāhur iva vāmanaḥ // Ragh_1.3 //atha vā kṛtavāgdvāre vaṃśe ‘smin pūrvasūribhiḥ /
maṇau vajrasamutkīrṇe sūtrasyevāsti me gatiḥ // Ragh_1.4 //
But the most nonchalant I’ve seen, thanks to Dr. Ganesh, is this gīti by Śrīkṛṣṇa Brahmatantra Yatīndra of the Parakāla Maṭha, Mysore:
nindatu vā nandatu vā
mandamanīṣā niśamya kṛtim etām
harṣaṃ vā marṣaṃ vā
sarṣapamātram api naiva vindema
Screw you guys. :-)
Big O() notation: a couple of sources
This post contains, just for future reference, a couple of primary sources relevant to the (“Big O”) notation:
- Some introductory words from Asymptotic Methods in Analysis by de Bruijn
- An letter from Donald Knuth on an approach to teaching calculus using this notation.
Visualizing product of permutations
A simple pedagogical trick that may come in handy: represent a permutation using arrows (curved lines) from to for each . Then, the product of two permutations can be represented by just putting the two corresponding figures (sets of arrows) one below the other, and following the arrows.
The figure is from an article called Symmetries by Alain Connes, found via the Wikipedia article on Morley’s trisector theorem (something entirely unrelated to permutations, but the article covers both of them and more).
I’m thinking how one might write a program to actually draw these: if we decide that the “height” of the figure is some , then each arrow needs to go from some to (using here the usual screen convention of coordinate increasing from left to right, and coordinate increasing from top to bottom). Further, each curve needs to have vertical slope at its two endpoints, so that successive curves can line up smoothly. The constraint on starting point, ending point, and directions at the endpoints defines almost a quadratic Bezier curve, except that here the two directions are parallel. So it’s somewhere between a quadratic and the (usual) cubic Bezier curve, which is given by the start point, end point, and derivatives at the start and end point. (Here we only care about the direction of the derivative; we can pick some arbitrary magnitude to fix the curve: the larger we pick, the more smooth it will look at the ends, at the cost of smoothness in the interior.)
Even knowing the curve, how do we generate an image?
The letter in Roister Doister
An early English example of resegmentation for change of meaning: Merygreeke’s letter to the Dame Custance, from Ralph Roister Doister (c. 1553), the first comedy to be written in the English language. [Aside: Shakespeare born in 1564 started had written all his plays before 1613, only 60 years from then.]
The example also shows that enjambment (no pause at end of line) did indeed exist in early English as well.
Scene 4
Sweete mistresse where as I loue you nothing at all, |
Scene 5
Sweete mistresse, where as I loue you, nothing at all |