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Experiments in Computer Science

Experiments in Computer Science. Experiments in Computer Science. " The fundamental principle of science, the definition almost, is this: the sole test of the validity of any idea is experiment" Richard P. Feynman

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Experiments in Computer Science

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  1. Experiments in Computer Science

  2. Experiments in Computer Science "The fundamental principle of science, the definition almost, is this: the sole test of the validity of any idea is experiment" • Richard P. Feynman • Tried and true experimental scientific methodology from Physics, Biology, Chemistry ... • Often not followed in Computer Science • Let's be better Computer Scientists!

  3. Scientific Methodology • Observe • (Devise solution) • Hypothesize • Design • Experiment • Analyze • Report

  4. Methodology: Observe and Understand • Find Problem • Test: make of Linux kernel • Build: memory intensive programs • Read: Linux Hacker’s guide says … • Understand Relationships • Hard page faults are expensive • Logical memory larger than physical

  5. Methodology: Devise and Hypothesize • Devise Solution (unless empirical) • Claypool Reliable Audio Protocol (CRAP) • Claypool buffering algorithm • Make Hypothesis • Generalization about relationships • Soft page faults are common • Malloc does not cause page fault • Needs to be tested (not proven)

  6. Methodology: Experiment • Design Experiment • Variable: variable workload • Control: baseline workload • Run Experiment “Whoa! That’s not what I expected!” • Bug in code • Back to “Run” • Uncontrolled event (system backup) • Back to “Design” • Insufficient understanding (Unix scheduling) • Back to “Understanding”

  7. Methodology: Analyze • Interpretation and Evaluation • Statistical significance • mean, confidence intervals, correlation, goodness of fit • Does data support or reject hypothesis? • Explanation of other phenomena • Better code reduces page faults, improves performance

  8. Graph: A Data Analysis Tool • A picture is worth a thousand words • Title, label axes (units!), legend

  9. Dirty Little Secrets • Mini-experiments (no, “Pilot Tests”) • Hypotheses after the fact • Running yields understanding • Results here mean results there • Controlled system still says meaningful things about the real world • Observing a system will not change it

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