Help with infinite while loop

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Devan
Devan 2012-11-24
I need to create a simple script that take a number, checks if it odd or even. If it's even: divide by two, if it's odd: multiply by 3 add 1. The script is supposed to repeat this check and calculation until the output reaches a value of one. I've tried the following while loop which calculates the first value but then infinity spits out this same value. Thanks in advance!
clear
disp('Please input student number')
ID = input('SI#: ');
if mod(ID,2) == 0
out = ID/2
else out = ID.*3+1
end
while out > 1
if mod(ID,2) == 0
out = ID/2
else out = ID.*3+1
end
end
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Matt J
Matt J 2012-11-24
OK. Glad I didn't spend my day trying to prove it :)
Jan
Jan 2012-11-25
编辑：Jan 2012-11-25
It is not proved. See http://en.wikipedia.org/wiki/Collatz_conjecture. You can earn 500$ and the Fields medal when you prove it, but this would conflict with the term " algorithmically undecidable".

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回答（3 个）

Matt Fig
Matt Fig 2012-11-24
编辑：Matt Fig 2012-11-24
The problem is that ID never changes in your loop so you are just doing the same thing over and over. Change all 'out' variables to 'ID' and your code should work fine.
Devan
Devan 2012-11-24
thanks!
Jan
Jan 2012-11-25
编辑：Jan 2012-11-25
It is a good idea to ask Google, in this case for "3N+1 Wiki". You find explanations, theorems, algorithms and visualizations, ... Enough material to solve the homework.

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