Lecture C13: Recurrence equations
Response to 'Muddiest Part of the Lecture Cards'
(40 respondents)
1)
What does Recurrnece Equations got to do with programming?
and similar questions (6 students)
Recurrence equations provide a means of expressing the cost of an algorithm as a function of the size of
the input. For example, with the Towers of Hanoi problem, moving 4 disks from tower 1 to tower 3 can
be broken down into:
●
Moving 3 disks from tower 1 to tower 2
●
Moving 1 disk from tower 1 to tower 3
●
Moving 3 disks from tower 2 to tower 3.
If the cost of solving n disks is T(n), from the above breakdown, we can express T(n) as:
C when n = 1
T(n)
=
2T(n1) + c when n >
1
This above representation is called a recurrence equation with T(n = 1) being the base case.
2)
What exactly does the cost of a procedure entail? What is the benefit of calculating the efficiency/
cost of a function?
and similar questions (5 students)
The cost of an algorithm can be measured in terms of memory usage, processor usage or a combination
of the two. When you are trying to compare the efficiency of two or more algorithms, you want to be
able to compute the cost of the problem as a function of the size of the problem. The two functions can
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 Winter '12
 CharlesColeman
 Aeronautics, Astronautics

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