Calculation with an algorithm

Question

Sorry I couldn't think of a good title.

I am working on a ICT related exercise and come across this:

Calculate alg a(n) and alg b(n) for n = 1,2,3,4 and 5

(a)
    alg_a(n):result
    if n > 1 then
    return(alg_a(n−1)+alg_a(n−1))
    else return(1)

(b)
    alg_b(n):result
    if n > 1 then
    return(2 · alg_b(n−1))
    else return(1)

At first, what does the code at line 1 do (alg_a(n):result)?

A: The question asks me to calculate alg a(n) so lets say I insert 1, if n > 1 --> no --> return 1. But what happens when I insert n = 2.

Any help is appreciated,

thanks!

What (programming) language is this? Please add that tag to the question =) — Josh Darnell
– Josh Darnell, Commented Jan 12, 2012 at 13:24
Since these functions are recursive, once you have a solution for n = 1 then you can use this to calculate the result for n = 2. And so on, for n = 3, 4, 5... — Paul R
– Paul R, Commented Jan 12, 2012 at 13:26
I have absolutely no idea which programming language this is. Most questions are written in pseudocode. — Jef
– Jef, Commented Jan 12, 2012 at 13:30

shift66 · Accepted Answer · 2012-01-12 14:37:02Z

6

algorithm alg_a(n) calculates 2^(n-1) and alg_b(n) does the same thing.
Theese are recursive functions. For example for 4 alg_a returns:
alg_a(4)=
alg_a(3) + alg_a(3) =
alg_a(2) + alg_a(2) + alg_a(2) + alg_a(2) =
alg_a(1) + alg_a(1) + alg_a(1) + alg_a(1) + alg_a(1) + alg_a(1) + alg_a(1) + alg_a(1) = 8

edited Jan 12, 2012 at 14:37

answered Jan 12, 2012 at 13:30

shift66

12k13 gold badges54 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

David M · Accepted Answer · 2012-01-12 13:32:00Z

3

This isn't code, it's some form of pseudo-code. The work "result" just means that what follows is the result of the function. So, alg_a(1) gives you the result of 1, whereas alg_a(2) gives you the result (alg_a(1) + alg_a(1)), i.e. 2. Continue to get your other answers.

The question in this case isn't asking for anything more complicated than the numeric answers.

answered Jan 12, 2012 at 13:32

David M

73.2k13 gold badges164 silver badges187 bronze badges

1 Comment

Jef Over a year ago

1 = 1 2 = 1*1+1*1 = 2 3 = 2*2+2*2 = 4 4 = 4*3+4*3 = 24 5 = 24*4+24*4 = 192 Is this correct?

Collectives™ on Stack Overflow

Calculation with an algorithm

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related