-----------------------------------

matt271

Wed Apr 08, 2009 7:35 pm


discrete math

-----------------------------------

there is no math section so i didnt know where to post this.

anywaysssssss i am just wondering if anybody can explain how to show two graphs are isomorphic?

i dont have the text book. but i did google it and i found this Wikipedia page http://en.wikipedia.org/wiki/Graph_isomorphism
i did it exactly like this example, but on my midterm the teacher took away points.

i went to ask why he took away points but there is a language barrier with this teacher.
all i gathered is that he wanted me to define some function like "f : a -> b" but i have never seen this format before.

my exam is tomorrow just wondering if anybody can explain it real quick??

this is a different question then was on my midterm but i think its more interesting because there's no graph:

Let T = {x|x divides 3} show that (T, +) and (Z, +) are isomorphic.


can i just say f(n) = 3n , n belongs to Z ?

ty


-----------------------------------

saltpro15

Wed Apr 08, 2009 7:55 pm


RE:discrete math

-----------------------------------

you can put it in off-topic, and I just finished gr10 math, so no idea, sorry :D


-----------------------------------

matt271

Wed Apr 08, 2009 8:07 pm


Re: RE:discrete math

-----------------------------------

you can put it in off-topic, and I just finished gr10 math, so no idea, sorry :D

got me all excited for nothing  :cry:  :cry:  :cry:  :cry: 

haha


-----------------------------------

Tony

Wed Apr 08, 2009 8:20 pm


Re: discrete math

-----------------------------------

he wanted me to define some function like "f : a -> b" but i have never seen this format before.
It's a one-to-one (injective) function. If you also define "f2 : b -> a" (onto (surjective)) then f and f2 create a bijection, which shows isomorphism of a and b.


-----------------------------------

matt271

Wed Apr 08, 2009 9:24 pm


RE:discrete math

-----------------------------------

k i got it :D ty ty :D:D


-----------------------------------

Brightguy

Thu Apr 09, 2009 3:31 am


Re: discrete math

-----------------------------------

It's a one-to-one (injective) function. If you also define "f2 : b -> a" (onto (surjective)) then f and f2 create a bijection, which shows isomorphism of a and b.
This shows |a|  T which preserves the addition structure, i.e., f(a+b)=f(a)+f(b).  You've found f, you just have to show it satisfies the necessary properties.  One way to show f is bijective is to give its inverse.

LaTeX is broken again?  You guys are killing me. :cry: