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#1 2012-05-16 06:29:01
- genericname
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- Registered: 2012-05-16
- Posts: 52
Question about Relations and Counting (Discrete Math)
What does the ''Anti-Reflexive'' property mean? My book defines it as "(x,x) !∈ R for all x ∈ S" I'm not sure what that means. Would it be right to say that it is the opposite of Reflexive?
Also I'm having problems with these practice problem(Counting):
What I got for my answers are:
a) 4*4*4*4 = 256
b) 3*3*3*3 = 81
c) 4*3*3*3 = 108
Are they correct?
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#2 2012-05-16 06:39:16
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
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Re: Question about Relations and Counting (Discrete Math)
The answer to your first question is yes,anti-reflexive is the opposite of reflexive. What the book is saying is that no element is in relation with itself. An example of such a relation is the 'not equal' relation.
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#3 2012-05-16 06:46:23
- genericname
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Re: Question about Relations and Counting (Discrete Math)
The answer to your first question is yes,anti-reflexive is the opposite of reflexive. What the book is saying is that no element is in relation with itself. An example of such a relation is the 'not equal' relation.
Oh, I think I got it now. So if, let's say S={0,1,2,3,4,5,6,7,8} and R= {(1,6), (2,7), (3,8), (6,1), (7,2), (8,3)} then R would be Anti-Reflexive and Symmetric?
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#4 2012-05-16 07:16:04
- anonimnystefy
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- Registered: 2011-05-23
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Re: Question about Relations and Counting (Discrete Math)
Yup! As long as it doesn't contain (1,1),(2,2),...,(8,8).
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#5 2012-05-16 13:45:39
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Question about Relations and Counting (Discrete Math)
Hi genericname;
a,b and c are correct! Welcome to the forum.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#6 2012-05-17 02:11:33
- genericname
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- Registered: 2012-05-16
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Re: Question about Relations and Counting (Discrete Math)
Thank you for the replies! Hope I'm ready for the final.
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#7 2012-05-17 04:33:56
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Question about Relations and Counting (Discrete Math)
Hi;
Good luck with your finals.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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