Paradoxes and theorems every developer should know

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1 Joshua Thijssen jaytaph

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Disclaimer: I'm not a (mad) scientist nor a mathematician. 2

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Second disclaimer: I will only tell lies 3

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German Tank Problem 4

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5 15

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6 53 72 8 15

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7 k = number of elements m = largest number

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72 + (72 / 4) - 1 = 89 8

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9 Intelligence Statistics Actual June 1940 1000 169 June 1941 1550 244 August 1942 1550 327 https://en.wikipedia.org/wiki/German_tank_problem

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9 Intelligence Statistics Actual June 1940 1000 169 June 1941 1550 244 August 1942 1550 327 https://en.wikipedia.org/wiki/German_tank_problem 122

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9 Intelligence Statistics Actual June 1940 1000 169 June 1941 1550 244 August 1942 1550 327 https://en.wikipedia.org/wiki/German_tank_problem 122 271

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9 Intelligence Statistics Actual June 1940 1000 169 June 1941 1550 244 August 1942 1550 327 https://en.wikipedia.org/wiki/German_tank_problem 122 271 342

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10 ➡ Data leakage.

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10 ➡ Data leakage. ➡ User-id's, invoice-id's, etc

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10 ➡ Data leakage. ➡ User-id's, invoice-id's, etc ➡ Used to approximate the number of iPhones sold in 2008.

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10 ➡ Data leakage. ➡ User-id's, invoice-id's, etc ➡ Used to approximate the number of iPhones sold in 2008. ➡ Calculate approximations of datasets with (incomplete) information.

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➡ Avoid (semi) sequential data to be leaked. ➡ Adding randomness and offsets will NOT solve the issue. ➡ Use UUIDs (better: timebased short IDs, you don't need UUIDs) 11

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12 Collecting (big) data is easy Analyzing big data is the hard part.

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Confirmation Bias 13

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2 4 6 14 Z={…,−2,−1,0,1,2,…}

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21% 15

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16 5 8 ? ? If a card shows an even number on one face, then its opposite face is blue.

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< 10% 17

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18 coke beer 35 17 If you drink beer then you must be 18 yrs or older.

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18 coke beer 35 17 If you drink beer then you must be 18 yrs or older.

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18 coke beer 35 17 If you drink beer then you must be 18 yrs or older.

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Cognitive Adaption for social exchange 19

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hint: Try and place your "technical problem" in a more social context. 20

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BDD 21

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22 5 8 ? ? If a card shows an even number on one face, then its opposite face is blue.

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22 5 8 ? ? If a card shows an even number on one face, then its opposite face is blue.

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22 5 8 ? ? If a card shows an even number on one face, then its opposite face is blue.

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TESTING 23

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24 ➡ Step 1: Write code ➡ Step 2: Write tests ➡ Step 3: Proﬁt

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public function isLeapYeap($year) { return ($year % 4 == 0); } 25 https://www.sundoginteractive.com/blog/confirmation-bias-in-unit-testing testIs1996ALeapYeap(); testIs2000ALeapYeap(); testIs2004ALeapYeap(); testIs2008ALeapYeap(); testIs2012ALeapYeap(); testIs1997NotALeapYear(); testIs1998NotALeapYear(); testIs2001NotALeapYear(); testIs2013NotALeapYear();

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public function isLeapYeap($year) { return ($year % 4 == 0); } 26 https://www.sundoginteractive.com/blog/confirmation-bias-in-unit-testing

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27 ➡ Tests where written based on actual code. ➡ Tests where written to CONFIRM actual code, not to DISPROVE actual code!

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28 TDD

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29 ➡ Step 1: Write tests ➡ Step 2: Write code ➡ Step 3: Proﬁt, as less prone to conﬁrmation bias (as there is nothing to bias!)

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Birthday paradox 30

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Question: 31 > 50% chance 4 march 18 september 5 december 25 juli 2 februari 9 october

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23 people 32

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366 persons = 100% 33

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Collisions occur more often than you realize 34

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Hash collisions 35

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16 bits means 300 values before >50% collision probability 36

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Watch out for: 37 ➡ Too small hashes. ➡ Unique data. ➡ Your data might be less "protected" as you might think.

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Heisenberg uncertainty principle 38

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It's not about star trek (heisenberg compensators) 39

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nor crystal meth 40

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41 x position p momentum (mass x velocity) ħ 0.0000000000000000000000000000000001054571800 (1.054571800E-34)

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The more precise you know one property, the less you know the other. 42

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This is NOT about observing! 43

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Observer effect 44 heisenbug

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It's about trade-offs 45

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Benford's law 46

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Numbers beginning with 1 are more common than numbers beginning with 9. 47

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Default behavior for natural numbers. 48

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find . -name \*.php -exec wc -l {} \; | sort | cut -b 1 | uniq -c 50

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find . -name \*.php -exec wc -l {} \; | sort | cut -b 1 | uniq -c 50 1073 1 886 2 636 3 372 4 352 5 350 6 307 7 247 8 222 9

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Bayesian filtering 52

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What's the probability of an event, based on conditions that might be related to the event. 53

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What is the chance that a message is spam when it contains certain words? 54

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55 P(A|B) P(A) P(B) P(B|A) Probability event A, if event B (conditional) Probability event A Probability event B Probability event B, if event A

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56 ➡ Figure out the probability a {mail, tweet, comment, review} is {spam, negative} etc.

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➡ 10 out of 50 comments are "negative". ➡ 25 out of 50 comments uses the word "horrible". ➡ 8 comments with the word "horrible" are marked as "negative". 57

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58 negative "horrible" 10 comments 25 comments 8 comments

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60 ➡ More words? ➡ Complex algorithm, ➡ but, we can assume that words are not independent from eachother ➡ Naive Bayes approach

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62 We must know beforehand which comments are negative?

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TRAINING SET 63

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64 "Your product is horrible and does not work properly. Also, you suck." "I had a horrible experience with another product. But yours really worked well. Thank you!" Negative: Positive:

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$trainingset = [ 'negative' => [ 'count' => 1, 'words' => [ 'product' => 1, 'horrible' => 1, 'properly' => 1, 'suck' => 1, ], ], 'positive' => [ 'count' => 1, 'words' => [ 'horrible' => 1, 'experience' => 1, 'product' => 1, 'thank' => 1, ], ], ]; 65

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66 $trainingset = [ 'negative' => [ 'count' => 631, 'words' => [ 'product' => 521, 'horrible' => 52, 'properly' => 36, 'suck' => 272, ], ], 'positive' => [ 'count' => 1263, 'words' => [ 'horrible' => 62, 'experience' => 16, 'product' => 311, 'great' => 363 'thank' => 63, ], ], ];

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67 ➡ You might want to ﬁlter stop-words ﬁrst. ➡ You might want to make sure negatives are handled property "not great" => negative. ➡ Bonus points if you can spot sarcasm.

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➡ Collaborative ﬁltering (mahout): ➡ If user likes product A, B and C, what is the chance that they like product D? 68

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69 Mess up your (training) data, and nothing can save you (except a training set reboot)

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➡ Binomial probability 70

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71 ➡ 30% change of acceptance for CFP ➡ 5 CFP's

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71 ➡ 30% change of acceptance for CFP ➡ 5 CFP's 1 - (0.7 * 0.7 * 0.7 * 0.7 * 0.7) = 1 - 0.168 = 0.832 83% on getting selected at least once!

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Ockham's Razor 72

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73 Among competing hypotheses, the one with the fewest assumptions should be selected.

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74 82 Everything should be made as simple as possible, but no simpler.

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YAGNI 75

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76 Actually, ➡ The principle of plurality Plurality should not be posited with necessity. ➡ The principle of parsimony It is pointless to do more with what is done with less.

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➡ Every element you add needs: design, development, maintenance, connectivity, support, etc etc. ➡ When "adding" elements, you are not adding, you are multiplying! 77

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78 Food for thought: Would Ockham accept a Service Oriented Architecture?

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http://farm1.static.ﬂickr.com/73/163450213_18478d3aa6_d.jpg 79

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80 Find me on twitter: @jaytaph Find me for development and training: www.noxlogic.nl / www.techademy.nl Find me on email: jthijssen@noxlogic.nl Find me for blogs: www.adayinthelifeof.nl