Repeated timings
Twenty timings range from 0.1 to 1.3 seconds. Their mean is 0.6 seconds, but their standard deviation is 0.31 seconds: the runs vary substantially. section 15.3
Standard deviation σ(S) measures how much observed timings depart from an ideal in which every run takes the same time. It has the same unit as the timings. Dividing it by the mean μ(S) gives the relative standard deviation; here, 0.31/0.6 is about 52%. section 15.3
TAKEAWAY: Relative standard deviation of run times should be in a low percentage range. A high value may signal a perturbed computation, unreliable measurement, or both; it does not identify which. section 15.3
Figure 15.1. Frequency histogram for our sample, showing the frequency with which each of the measured values was obtained
The frequency histogram makes the spread of the twenty measured timings visible. section 15.3
