Paradoxes and theorems every developer should know

Transcript

1. 1 Joshua Thijssen jaytaph <?php namespace

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

3. Second disclaimer: I will only tell lies 3

4. German Tank Problem 4

5. 5

6. 5 15

7. 6

8. 6 53 72 8 15

9. 7 k = number of elements m = largest number

10. 72 + (72 / 4) - 1 = 89 8

11. 9 Intelligence Statistics Actual June 1940 1000 169 June 1941

    1550 244 August 1942 1550 327 https://en.wikipedia.org/wiki/German_tank_problem

12. 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

13. 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

14. 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

15. 10

16. 10 ➡ Data leakage.

17. 10 ➡ Data leakage. ➡ User-id's, invoice-id's, etc

18. 10 ➡ Data leakage. ➡ User-id's, invoice-id's, etc ➡ Used

    to approximate the number of iPhones sold in 2008.

19. 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.

20. ➡ 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

21. 12 Collecting (big) data is easy Analyzing big data is

    the hard part.

22. Confirmation Bias 13

23. 2 4 6 14 Z={…,−2,−1,0,1,2,…}

24. 21% 15

25. 16 5 8 ? ? If a card shows an

    even number on one face, then its opposite face is blue.

26. < 10% 17

27. 18 coke beer 35 17 If you drink beer then

    you must be 18 yrs or older.

28. 18 coke beer 35 17 If you drink beer then

    you must be 18 yrs or older.

29. 18 coke beer 35 17 If you drink beer then

    you must be 18 yrs or older.

30. Cognitive Adaption for social exchange 19

31. hint: Try and place your "technical problem" in a more

    social context. 20

32. BDD 21

33. 22 5 8 ? ? If a card shows an

    even number on one face, then its opposite face is blue.

34. 22 5 8 ? ? If a card shows an

    even number on one face, then its opposite face is blue.

35. 22 5 8 ? ? If a card shows an

    even number on one face, then its opposite face is blue.

36. TESTING 23

37. 24 ➡ Step 1: Write code ➡ Step 2: Write

    tests ➡ Step 3: Profit

38. 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();

39. 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();

40. public function isLeapYeap($year) { return ($year % 4 == 0);

    } 26 https://www.sundoginteractive.com/blog/confirmation-bias-in-unit-testing

41. 27 ➡ Tests where written based on actual code. ➡

    Tests where written to CONFIRM actual code, not to DISPROVE actual code!

42. 28 TDD

43. 29 ➡ Step 1: Write tests ➡ Step 2: Write

    code ➡ Step 3: Profit, as less prone to confirmation bias (as there is nothing to bias!)

44. Birthday paradox 30

45. Question: 31 > 50% chance 4 march 18 september 5

    december 25 juli 2 februari 9 october

46. 23 people 32

47. 366 persons = 100% 33

48. Collisions occur more often than you realize 34

49. Hash collisions 35

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

51. Watch out for: 37 ➡ Too small hashes. ➡ Unique

    data. ➡ Your data might be less "protected" as you might think.

52. Heisenberg uncertainty principle 38

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

54. nor crystal meth 40

55. 41 x position p momentum (mass x velocity) ħ 0.0000000000000000000000000000000001054571800

    (1.054571800E-34)

56. The more precise you know one property, the less you

    know the other. 42

57. This is NOT about observing! 43

58. Observer effect 44 heisenbug

59. It's about trade-offs 45

60. Benford's law 46

61. Numbers beginning with 1 are more common than numbers beginning

    with 9. 47

62. Default behavior for natural numbers. 48

63. 49

64. find . -name \*.php -exec wc -l {} \; |

    sort | cut -b 1 | uniq -c 50

65. 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

66. 51

67. Bayesian filtering 52

68. What's the probability of an event, based on conditions that

    might be related to the event. 53

69. What is the chance that a message is spam when

    it contains certain words? 54

70. 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

71. 56 ➡ Figure out the probability a {mail, tweet, comment,

    review} is {spam, negative} etc.

72. ➡ 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

73. 58 negative "horrible" 10 comments 25 comments 8 comments

74. 59

75. 60 ➡ More words? ➡ Complex algorithm, ➡ but, we

    can assume that words are not independent from eachother ➡ Naive Bayes approach

76. 61

77. 62 We must know beforehand which comments are negative?

78. TRAINING SET 63

79. 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:

80. $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

81. 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, ], ], ];

82. 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.

83. ➡ Collaborative filtering (mahout): ➡ If user likes product A,

    B and C, what is the chance that they like product D? 68

84. 69 Mess up your (training) data, and nothing can save

    you (except a training set reboot)

85. ➡ Binomial probability 70

86. 71 ➡ 30% change of acceptance for CFP ➡ 5

    CFP's

87. 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!

88. Ockham's Razor 72

89. 73 Among competing hypotheses, the one with the fewest assumptions

    should be selected.

90. 74 82 Everything should be made as simple as possible,

    but no simpler.

91. YAGNI 75

92. 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.

93. ➡ Every element you add needs: design, development, maintenance, connectivity,

    support, etc etc. ➡ When "adding" elements, you are not adding, you are multiplying! 77

94. 78 Food for thought: Would Ockham accept a Service Oriented

    Architecture?

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

96. 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