Notices by Stephen Michael Kellat (alpacaherder@quitter.se), page 10

Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Wednesday, 31-Jan-2018 22:14:23 EST Stephen Michael Kellat

ALL HANDS, ALL HANDS, PUTTING TIME ON THE CLOCK. SECURE TO DAMAGE CONTROL STATIONS AT X MINUS 12 HOURS.
https://www.timeanddate.com/countdown/generic?p0=263&iso=20180208T235959&year=2018&month=2&day=8&hour=23&min=59&sec=59&msg=Continuing%20Resolution%20Lapses&csz=1

In conversation Wednesday, 31-Jan-2018 22:14:23 EST from mastodon.sdf.org permalink Repeated by alpacaherder
Stephen Michael Kellat (alpacaherder@quitter.se)'s status on Wednesday, 31-Jan-2018 22:09:14 EST Stephen Michael Kellat
in reply to
- Annah
- awavauatush
@maiyannah @ninjawedding Why on Earth would we ever do that? We barely schedule a month at a time on activities...

In conversation Wednesday, 31-Jan-2018 22:09:14 EST from quitter.se permalink
Stephen Michael Kellat (alpacaherder@quitter.se)'s status on Wednesday, 31-Jan-2018 06:31:50 EST Stephen Michael Kellat
- Elly, nasty enby :heart_pan:
@elizafox To which mother would reply: "What mickey did you slip him?"

In conversation Wednesday, 31-Jan-2018 06:31:50 EST from quitter.se permalink
Stephen Michael Kellat (alpacaherder@quitter.se)'s status on Wednesday, 31-Jan-2018 06:29:00 EST Stephen Michael Kellat
in reply to
- lnxw48a1
- zoowar
@lnxw48a1 @zoowar Mary Jane usage is contraindicated by all the medications I'm on. Induced psychosis would be the least of my worries...

In conversation Wednesday, 31-Jan-2018 06:29:00 EST from quitter.se permalink
Hacker News ( unofficial ) (hackernews@pod.jpope.org)'s status on Tuesday, 30-Jan-2018 02:00:12 EST Hacker News ( unofficial )

A sample of brilliance

Hacker News Comments: https://news.ycombinator.com/item?id=16263288

Source: https://blog.acolyer.org/2018/01/30/a-sample-of-brilliance/

#hackernews
In conversation Tuesday, 30-Jan-2018 02:00:12 EST from pod.jpope.org permalink Repeated by alpacaherder
Attachments
1. A sample of brilliance
  
  By adriancolyer from the morning paper
  A sample of brilliance Jon Bentley et al., CACM 1987
  
  (Also available in )
  
  Jon Bentley’s “Programming Pearls” was a well-loved column in CACM (and also available in book form). Today we’re taking at look at his “Sample of Brilliance” column from 1987, featuring guest contributions from none other then Bob Floyd (whose Turing Award lecture we reviewed yesterday). It’s a chance to see Floyd’s algorithm development skills in action.
  
  An earlier Jon Bentley column (December 1984) had discussed sampling algorithms. By sampling here we mean drawing a random sample without replacement. For example, dealing a hand of 5 cards (out of the 52 in a deck). Let’s assume we have to hand a function RandInt(I,J) that returns an integer uniformly distributed over I..J as a building block. For example, in JavaScript:
  
  function randInt(i,j) { return i + Math.floor(Math.random() * j); }
  
  The sampling algorithm from the 1984 column, algorithm ‘S’, worked as follows:
  
  Here’s a JavaScript rendition:
  
  /* sample m integers from n */ function sampleS(m, n) { let s = new Set(); while(s.size < m) { s.add(randInt(1,n); } return s; }
  
  Algorithm S has many virtues: it is correct, fairly efficient, and remarkably succinct. It is so good, as a matter of fact, that I thought one couldn’t do better. In the December 1984 column I therefore charged ahead and described it in detail. Unfortunately I was wrong; fortunately, Bob Floyd caught me sleeping.
  
  What had caught Floyd’s eye, was the case when N = M = 100. Suppose you have already drawn 99 random numbers, there is only one possible choice for the last one! And yet algorithm S will carry on blindly drawing random numbers until it hits by chance on that special last number. Is there an algorithm that uses exactly one call of RandInt for each random number in S?
  
  Floyd’s key rule in this problem was, in his own words, to “look for a mathematical characterization of the solution before you think about an algorithm to obtain it.”
  
  This led him to Algorithm F1:
  
  With a fairly direct translation in JavaScript as follows:
  
  function sampleF1(m, n) { let s = new Set(); if (m !== 0) { s = sampleF1(m-1, n-1); const t = randInt(1, n); s.add( s.has(t) ? n : t ); } return s; }
  
  We can appreciate the correctness of Floyd’s algorithm anecdotally. When M=5 and N=10, the algorithm first recursively computes in S a 4-element random sample from 1..9. Next it assigns to T a random integer in the range 1..10. Of the 10 values that T can assume, exactly 5 result in inserting 10 into S: the four values already in S, and the value 10 itself. Thus element 10 is inserted into the set with the correct probability of 5/10.
  
  (You could construct a nice inductive proof based on those observations).
  
  I’m sure you’ve noticed another inefficiency though – we’re creating a lot of Set objects! By introducing a temporary variable J, Floyd was able to eliminate the recursion and give an iterative algorithm almost as succinct as Algorithm S:
  
  In JavaScript:
  
  function sampleF2(m, n) { let s = new Set(); for (let j = n - m + 1; j <= n; j++) { const t = randInt(1, j); s.add( s.has(t) ? j : t ); } return s; }
  
  Let’s do a run with M=3 and N=10…
  
  M = 3, N = 10, S = {} Iteration 1: J = 8 Draw T = 7 S = {7} Iteration 2: J = 9 Draw T = 4 S = {7, 4} Iteration 3: J = 10 Draw T = 7 // again S = {7, 4, 10}
  
  I averaged the results of 10 runs each of algorithms S, F1, and F2, and you can clearly see the superiority of F2 as N gets larger (times are in ms on my laptop, ALG F1 runs out of stack when N is 100,00):
  
  N ALG S (N,N) ALG F1 (N,N) ALG F2 (N,N)
  10 0.32 0.18 0.17
  100 5.24 0.80 0.60
  1,000 7.84 3.42 2.09
  10,000 68.96 15.76 12.79
  100,000 1,063.54 – 168.87
  1,000,000 35,831.82 – 3,652.89
  If we’re interested not just in a random set, but also that the elements of the sample occur in a random order, then Algorithm F2 isn’t perfect. Notice that if we draw a random number we’ve seen before, we add J in increasing order with each iteration. Interestingly, the documentation for JavaScript’s Set also over specifies (in my view) what will happen when you iterate over set members – they are returned in the order you added them.
  
  For the final piece of the puzzle therefore, Floyd gives us ‘Algorithm P’, a way of generating a random permutation.
  
  To compute an M-element permutation from 1..N, it first computes an (M-1) element permutation from 1..N-1; a recursive version of the algorithm eliminates the variable J.
  
  In JavaScript:
  
  function permute(m, n) { let s = new Array(); for (let j = n - m + 1; j <= n; j++) { const t = randInt(1,j); const i = s.indexOf(t); if (i === -1) { s.splice(0, 0, t); } else { s.splice(i+1, 0, j); } } return s; }
  
  Doug McIlroy found an elegant way to show this is correct: “there is one and only one way to produce each permutation, because the algorithm can be run backward.”
  
  Consider the case with M=5, N=10, and the final sequence is 7 2 9 1 5. Because 10 (the final value of J) does not occur in S, the previous sequence must have been 2 9 1 5, and randInt returned T = 7. Keep following the chain, and you can recover the entire sequence of random values. And therefore, “because all random sequences are (supposedly) equally likely, all permutations are also.”
  
  Algorithm S is a pretty good algorithm, but not good enough for Bob Floyd. Not content with its inefficiency, he developed optimal algorithms for generating random samples and random permutations. His programs are a model of efficiency, simplicity, and elegance.
  
  Following his mathematical analysis of the problem, and after conceiving Algorithm P, Floyd recalled, “I knew it was right even before I proved it.” But note that he did indeed go on to prove it!
  
  If you want to play with these algorithms some more, the original column (link at the top of this post) contains a set of eight problems that will have you reasoning about different implementations of Sets and Sequences, as well as proofs of correctness.
zerohedge (zerohedge@quitter.im)'s status on Tuesday, 30-Jan-2018 06:09:50 EST zerohedge

FBI Director Wray "Shocked To His Core" By FISA Memo, McCabe 'Removed' Next Day, More Heads To Roll: Report https://quitter.im/url/891834
In conversation Tuesday, 30-Jan-2018 06:09:50 EST from quitter.im permalink Repeated by alpacaherder
Attachments
1. FBI Director Wray "Shocked To His Core" By FISA Memo, McCabe 'Removed' Next Day, More Heads To Roll: Report
  
  from Zero Hedge
Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Sunday, 28-Jan-2018 17:58:23 EST Stephen Michael Kellat

Handbasket Preview:
https://twitter.com/stillgray/status/957634744023306240?s=09

In conversation Sunday, 28-Jan-2018 17:58:23 EST from mastodon.sdf.org permalink Repeated by alpacaherder
Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Sunday, 28-Jan-2018 17:18:10 EST Stephen Michael Kellat

And this is how we're going to Hell:
https://twitter.com/antoniogm/status/956657889963270144?s=09

In conversation Sunday, 28-Jan-2018 17:18:10 EST from mastodon.sdf.org permalink Repeated by alpacaherder
zerohedge (zerohedge@quitter.im)'s status on Monday, 29-Jan-2018 11:53:46 EST zerohedge

Trump Administration Says It Has "No Plans" To Build "Nationalized" 5G Network https://quitter.im/url/890149
In conversation Monday, 29-Jan-2018 11:53:46 EST from quitter.im permalink Repeated by alpacaherder
Attachments
1. Trump Administration Says It Has "No Plans" To Build "Nationalized" 5G Network
  
  from Zero Hedge
Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Monday, 29-Jan-2018 01:20:50 EST Stephen Michael Kellat

LaTeXML \itemize creates weird <ul>
https://tex.stackexchange.com/q/352634/61956

In conversation Monday, 29-Jan-2018 01:20:50 EST from mastodon.sdf.org permalink Repeated by alpacaherder
Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Sunday, 28-Jan-2018 22:16:16 EST Stephen Michael Kellat
- Craig Maloney ☕
@craigmaloney HAHAHAHAHAHAHAHAHA The shutdown only went Saturday, Sunday, Monday last week. A new Continuing Resolution was adopted that expires on **February 8th** which is a Thursday and also when the 2018 Winter Olympics start. It wasn't solved but there was a truce. See my blog post here: http://skellat.freeshell.org/blog/damage-report.html

In conversation Sunday, 28-Jan-2018 22:16:16 EST from mastodon.sdf.org permalink Repeated by alpacaherder
Stephen Michael Kellat (skellat@mastodon.sdf.org)'s status on Sunday, 28-Jan-2018 22:14:09 EST Stephen Michael Kellat
- Craig Maloney ☕
@craigmaloney That'll be the time to start putting together a co-op to buy a shortwave radio station perhaps. Radio licensing fees are privileged compared to streaming.

In conversation Sunday, 28-Jan-2018 22:14:09 EST from mastodon.sdf.org permalink Repeated by alpacaherder