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UNDERSTANDING SOFTWARE DEV WITH EQUATIONS
- 1. UNDERSTANDING SOFTWARE DEV USING EQUATIONS jacques@nreality.com @jacdevos
- 3. β’ Hard! β’ Non-intuitive β’ Misunderstood β’ Seen as black-art done by amateurs Software engineering is:
- 4. Iβm not a mathematician
- 5. Mental models, rather than precise calculations
- 6. Why do systems get so complicated?
- 7. Handing complexity with π π β π π
- 8. 10 1 2 34 5
- 9. π π β π π
- 11. Complexity is caused by: quadratic increase in connections
- 12. How do we reduce complexity?
- 16. Summary:
- 17. What is the effect of messy code?
- 18. Go slow to go fast with π» π = πΆ(π)
- 19. 0 50 100 150 200 250 300 10 20 30 40 50 60 70 80 90 100 TIME+RISKTOMAKECHANGE FEATURES BUILT CODE CHANGE COMPLEXITY O(n) O(n2)
- 20. Clean Code gives β’ Easy to read β’ SOLID design β’ Boy scout refactoring β’ Self-testing β’ TDD πΆ(π)
- 21. Messy code gives β’ Manual regression testing β’ Spaghetti dependencies β’ Hart to understand πΆ(π π )
- 22. Your algorithm of work determines order of time complexity
- 23. In summary
- 24. Weβre so busy! Why donβt we get stuff done?
- 26. Maximise efficiency with ππππ = πΊππππ . π«ππππππ
- 29. 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 0 20 40 60 80 100 120 140 50 100 150 200 250 300 350 400 450 500 FLOWRATE(VEHICLES/HOUR) SPEED(KILOMETER/HOUR) DENSITY (VEHICLES/KILOMETER) OPTIMAL FLOW Speed (Km/h) Flow (Vehicles/h) UnstableStable Speed decreases as density increases. This is not intuitive. Optimum flow at speed 60 and density 250. Neither MAXED!
- 30. Speed = (1 β Density . JamDens) . MaxSpeed
- 31. How does this apply to software? β’ πΉπππ€ = πππππ. π·πππ ππ‘π¦ β’ Velocity = Throughput = Flow (avg # features delivered per week) β’ WIP = Density (avg # features started but not completed) β’ πΆπ¦πππ π‘πππ = 1 πππππ (avg time it takes to complete a feature) β’ πβππ’πβππ’π‘ = ππΌπ πΆπ¦πππ ππππ (aka Littleβs Law) π½πππππππ = π¨ππ ππππππππ ππ ππππππππ π¨ππ ππππ ππ ππππππππ π πππππππ
- 32. In summary
- 34. Improve continuously with π¨ = π·π ππ
- 36. β’ r = -1% per week (decay rate) β’ t = 104 weeks/2 years (time in weeks) This gives us β’ 34% of original β’ Degraded 66% over 2 years! Is this how technical debt behaves? π ππ
- 37. β’ r = 1% per week (improvement rate) β’ t = 104 weeks/2 years (time in weeks) This gives us β’ 294% improvement over 2 years! π°ππππππππππ = π ππ
- 38. In summary
- 39. Simplify by removing dependencies Go slow to go fast Remove congestion to flow Continuous improvement compounds
- 40. Other equations β’ Entropy β’ Bayesian Inference β’ The software engineering equation β’ Yours?
Editor's Notes
- Not an abstract theoretical construct.
- https://en.wikipedia.org/wiki/Metcalfe%27s_law
- Metcalfe's law β Net work
- Both!
- Note: things that change together
- Β Big O notation: the algorithm hasΒ order of n2Β time complexity Code change complexity/speed The way we work determines the difficulty in changes over time Donβt just optimise for short term Common trap: the way we work slows us down in the long term O(n2) - difficulty in building new feature safely if no test - O(logn) - the speed you can add new features if you donβt test or refactor. O(n) - can it scale? - apply to process, code, structure - SELF TEST GIVES O(n) - not test gives O(n2) We donβt have time to write tests. We need to get this out quickly! We can worry about quality later. Inspired by (but a different take on it): https://michaelfeathers.silvrback.com/code-change-complexity
- Credit : www.improvetraffic.org Worldβs largest traffic jam in Chine β 100km, 11 days
- Fundamental Relations of Traffic Flow https://www.civil.iitb.ac.in/tvm/1111_nptel/512_FundRel/plain/plain.html https://en.wikipedia.org/wiki/Fundamental_diagram_of_traffic_flow
- When density goes up β speed goes down
- When density goes up β speed goes down
- Also known as little's law
- Are we appreciating or depreciating Letβs start improving Common trap: we are too busy to improve https://www.youtube.com/watch?v=o5QRdHH8aeQ htps:/t/en.wikipedia.org/wiki/Compound_interest#Mathematics_of_interest_rates
- http://jamesclear.com/marginal-gains
- http://www.mathwarehouse.com/calculators/continuous-compound-interest-calculator.php
- http://www.mathwarehouse.com/calculators/continuous-compound-interest-calculator.php
- Are we appreciating or depreciating Letβs start improving Common trap: we are too busy to improve