bounding least common multiples with triangles
play

Bounding Least Common Multiples with Triangles ITP 2016: Proof Pearl - PowerPoint PPT Presentation

Bounding Least Common Multiples with Triangles ITP 2016: Proof Pearl Hing-Lun Chan and Michael Norrish College of Engineering and Computer Science Australian National University August 2016, Nancy, France. Hing-Lun Chan & Michael Norrish


  1. Bounding Least Common Multiples with Triangles ITP 2016: Proof Pearl Hing-Lun Chan and Michael Norrish College of Engineering and Computer Science Australian National University August 2016, Nancy, France. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 1 / 21

  2. Motivation AKS mechanisation AKS mechanisation Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 2 / 21

  3. Motivation AKS mechanisation AKS mechanisation Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 2 / 21

  4. Motivation AKS mechanisation AKS mechanisation ◦ Replacing 2 m by 2 m / 2 makes the lower bound valid for all m > 0. ◦ This change won’t affect the conclusion: AKS algorithm is in class P . Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 2 / 21

  5. Motivation AKS mechanisation Nair’s Paper Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 3 / 21

  6. Motivation AKS mechanisation Nair’s Paper Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 3 / 21

  7. Motivation AKS mechanisation Nair’s Paper ◦ The cryptic “difference operator” means Leibniz’s Harmonic Triangle! Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 3 / 21

  8. LCM of Consecutive Numbers LCM of Consecutive Numbers LCM of a List list_lcm [1] list_lcm [1; 2] list_lcm [1; 2; 3] list_lcm [1; 2; 3; 4] list_lcm [1; 2; 3; 4; 5] list_lcm [1; 2; 3; 4; 5; 6] Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 4 / 21

  9. LCM of Consecutive Numbers LCM of Consecutive Numbers LCM of a List list_lcm [1] = 1 list_lcm [1; 2] = 2 list_lcm [1; 2; 3] = 6 list_lcm [1; 2; 3; 4] = 12 list_lcm [1; 2; 3; 4; 5] = 60 list_lcm [1; 2; 3; 4; 5; 6] = 60 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 4 / 21

  10. LCM of Consecutive Numbers LCM of Consecutive Numbers LCM of a List ≥ 2 0 = 1 list_lcm [1] = 1 ≥ 2 1 = 2 list_lcm [1; 2] = 2 ≥ 2 2 = 4 list_lcm [1; 2; 3] = 6 ≥ 2 3 = 8 list_lcm [1; 2; 3; 4] = 12 ≥ 2 4 = 16 list_lcm [1; 2; 3; 4; 5] = 60 ≥ 2 5 = 32 list_lcm [1; 2; 3; 4; 5; 6] = 60 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 4 / 21

  11. LCM of Consecutive Numbers LCM of Consecutive Numbers LCM of a List ≥ 2 0 = 1 list_lcm [1] = 1 ≥ 2 1 = 2 list_lcm [1; 2] = 2 ≥ 2 2 = 4 list_lcm [1; 2; 3] = 6 ≥ 2 3 = 8 list_lcm [1; 2; 3; 4] = 12 ≥ 2 4 = 16 list_lcm [1; 2; 3; 4; 5] = 60 ≥ 2 5 = 32 list_lcm [1; 2; 3; 4; 5; 6] = 60 Theorem Lower bound for the LCM of consecutive numbers. ⊢ 2 n ≤ list_lcm [ 1 .. n + 1 ] Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 4 / 21

  12. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound Let ℓ = [ a ; b ; c ] . Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 5 / 21

  13. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound Let ℓ = [ a ; b ; c ] . Since LCM is a common multiple of each element (in fact, the least), a ≤ list_lcm [ a ; b ; c ] b ≤ list_lcm [ a ; b ; c ] c ≤ list_lcm [ a ; b ; c ] Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 5 / 21

  14. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound Let ℓ = [ a ; b ; c ] . Since LCM is a common multiple of each element (in fact, the least), a ≤ list_lcm [ a ; b ; c ] b ≤ list_lcm [ a ; b ; c ] c ≤ list_lcm [ a ; b ; c ] Hence a + b + c ≤ 3 × list_lcm [ a ; b ; c ] Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 5 / 21

  15. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound Let ℓ = [ a ; b ; c ] . Since LCM is a common multiple of each element (in fact, the least), a ≤ list_lcm [ a ; b ; c ] b ≤ list_lcm [ a ; b ; c ] c ≤ list_lcm [ a ; b ; c ] Hence a + b + c ≤ 3 × list_lcm [ a ; b ; c ] Theorem For a list ℓ of positive numbers, SUM ℓ ≤ LENGTH ℓ × list_lcm ℓ . Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 5 / 21

  16. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound – Applications Theorem For a list ℓ of positive numbers, SUM ℓ ≤ LENGTH ℓ × list_lcm ℓ . Naïve application: ( n + 1 )( n + 2 ) ≤ ( n + 1 ) × list_lcm [ 1 .. n + 1 ] 2 ( n + 2 ) ≤ list_lcm [ 1 .. n + 1 ] 2 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 6 / 21

  17. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound – Applications Theorem For a list ℓ of positive numbers, SUM ℓ ≤ LENGTH ℓ × list_lcm ℓ . Naïve application: ( n + 1 )( n + 2 ) ≤ ( n + 1 ) × list_lcm [ 1 .. n + 1 ] 2 ( n + 2 ) disappointing! ≤ list_lcm [ 1 .. n + 1 ] 2 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 6 / 21

  18. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Lower Bound – Applications Theorem For a list ℓ of positive numbers, SUM ℓ ≤ LENGTH ℓ × list_lcm ℓ . Naïve application: ( n + 1 )( n + 2 ) ≤ ( n + 1 ) × list_lcm [ 1 .. n + 1 ] 2 ( n + 2 ) disappointing! ≤ list_lcm [ 1 .. n + 1 ] 2 Need a clever idea to obtain this lower bound: 2 n ≤ list_lcm [ 1 .. much better! n + 1 ] Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 6 / 21

  19. LCM of Consecutive Numbers LCM Lower Bound for a List LCM Bound Comparison list_lcm [ 1 .. n + 1 ] 10 3 2 n ( n + 2 ) / 2 10 2 10 1 10 0 0 2 4 6 8 n Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 7 / 21

  20. Triangles Pascal’s Triangle Yang Hui’s Triangle Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 8 / 21

  21. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  22. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 1 1 1 1 2 1 1 1 1 3 3 1 1 1 1 4 6 4 1 1 1 1 5 10 10 5 1 1 1 1 6 15 20 15 6 1 1 Each boundary entry: always 1. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  23. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 1 2 2 1 1 3 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1 Each boundary entry: always 1. Each inside entry: sum of two immediate parents. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  24. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 2 1 1 3 3 1 1 4 4 6 6 4 1 1 5 10 10 10 5 1 1 6 15 20 15 6 1 Each boundary entry: always 1. Each inside entry: sum of two immediate parents. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  25. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 10 5 5 1 1 6 15 20 15 15 6 1 Each boundary entry: always 1. Each inside entry: sum of two immediate parents. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  26. Triangles Pascal’s Triangle Pascal’s Triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 1 6 6 15 15 20 20 15 15 6 6 1 1 Each boundary entry: always 1. Each inside entry: sum of two immediate parents. Sum of the n -th row: n � n � = ( 1 + 1 ) n = 2 n � k k = 0 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 9 / 21

  27. Triangles Leibniz’s Triangle Leibniz’s Harmonic Triangle 1 1 1 1 2 2 1 1 1 3 6 3 1 1 1 1 4 12 12 4 1 1 1 1 1 5 20 30 20 5 1 1 1 1 1 1 6 30 60 60 30 6 1 1 1 1 1 1 1 7 42 105 140 105 42 7 Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 10 / 21

  28. Triangles Leibniz’s Triangle Leibniz’s Harmonic Triangle 1 1 1 1 1 1 1 1 2 2 2 2 1 1 1 1 1 3 3 6 3 3 1 1 1 1 1 1 4 4 12 12 4 4 1 1 1 1 1 1 1 5 5 20 30 20 5 5 1 1 1 1 1 1 1 1 6 6 30 60 60 30 6 6 1 1 1 1 1 1 1 1 1 7 7 42 105 140 105 42 7 7 1 Each boundary entry: for the n -th row, n = 0 , 1 , · · · ( n + 1 ) Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 10 / 21

  29. Triangles Leibniz’s Triangle Leibniz’s Harmonic Triangle 1 1 1 1 1 2 2 2 1 1 1 1 1 3 3 6 6 3 1 1 1 1 4 12 12 4 1 1 1 1 1 5 20 30 20 5 1 1 1 1 1 1 6 30 60 60 30 6 1 1 1 1 1 1 1 7 42 105 140 105 42 7 1 Each boundary entry: for the n -th row, n = 0 , 1 , · · · ( n + 1 ) Each entry (inside or not): sum of two immediate children. Hing-Lun Chan & Michael Norrish (ANU) Bounding LCM with Triangles ITP 2016 10 / 21

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend