Andrew S. Tanenbaum (OS) Edition 4 Exercise 2 Question 49 (Page No. 178)

Question

The aging algorithm with $a = 1/2$ is being used to predict run times. The previous four runs, from oldest to most recent, are $40, 20, 40,$ and $15$ msec. What is the prediction of the next time?

Answer 1

On taking all the $4$ previous run times, the prediction

$\begin {align} =& (((40 + 20) / 2 + 40) /2 +15) / 2 \\ =& ((30 + 40 / 2 + 15 ) /2  \\=& (35 + 15)/2 \\=& 25 \end {align}$

On taking only $2$ previous executions, the prediction$ = \frac{40 + 15}{2} = 27.5$

Comments

`JEET
Sir, to get the answer we also need the predicted times for the last four runs as well or at least the predicted time of the oldest run, Because the formula in ageing is this: T(n) = a*t(n-1) + (1-a)T(n-1)

What do u say?