1,077 reputation
1611
bio website faculty.capebretonu.ca/jpreen
location Nova Scotia, Canada
age 47
visits member for 3 years, 5 months
seen 5 hours ago

Graph Theorist with an interest in most areas of pure maths.


Dec
9
awarded  Caucus
Dec
4
comment Question on Graphs?
Note that when using open neighbourhoods of vertex sets it can be awkward to have some elements of $A$ in $N(A)$ and some not in $N(A)$ as can happen with this definition. I prefer to use a definition in terms of closed neighbourhoods as follows: $N(A) := (\bigcup_{v\in A} N[v] ) \setminus A$, where $N[v]:=\{v\} \cup N(v)$.
Oct
17
answered Maple not displaying graph
Sep
8
answered Smallest non-hamiltonian k-connected graph
Aug
6
comment How many distinct chromatic polynomials are there for simple connected graphs?
so are you looking for the numbers of different chromatic polynomials or the numbers of graphs with unique chromatic polynomials?
Aug
6
comment How many distinct chromatic polynomials are there for simple connected graphs?
@Jernej I thought your answer was useful and may even be what Hooked was looking for, hopefully we will find out!
Aug
5
comment How many distinct chromatic polynomials are there for simple connected graphs?
I have verified the above numbers for general graphs up to 8 vertices and for connected graphs the sequence of chromatically unique graphs is 1, 1, 2, 4, 10, 27, 100, 570.
Aug
5
comment How many distinct chromatic polynomials are there for simple connected graphs?
The definition given at mathworld.wolfram.com/ChromaticallyUniqueGraph.html is that this sequence lists the number of graphs which have a unique polynomial, not the number of different polynomials...
Jul
8
comment Software to find out adjacency matrix of a graph.
There are shortcuts using the underlined letters, so alt V to get to the vertex menu, etc. I've never needed edge colouring, so didn't implement it, sorry. It should be possible to add it with a bit of coding knowledge though.
Jul
8
comment Software to find out adjacency matrix of a graph.
Sorry, no manual, but if there's something that doesn't do what you think, feel free to ask here.
Jul
5
awarded  Yearling
Jun
20
revised The number of dominating sets of a bipartite graph is not exactly divisible by $2$
Tidied up the flow
Jun
20
answered The number of dominating sets of a bipartite graph is not exactly divisible by $2$
Jun
15
comment The most efficient method for generating new prime numbers
This sequence is the (2nd) Euclid-Mullin sequence: oeis.org/A000946
Jun
9
comment Find the chromatic polynomial of the following graph
Your answer is correct, but your reasoning isn't; you have to consider vertex 3 before 4 and 6 before 7, since you haven't coloured 3 before colouring 4 in your way it has only 1 pre-coloured neighbour at that time...
May
23
revised Chromatic recurrence
added 91 characters in body
May
23
revised Chromatic recurrence
added 16 characters in body
May
23
answered Chromatic recurrence
May
21
comment Help me calculating chromatic polynomial of this subgraph
It works only if the intersection is a clique, you can even use a split of $ABCD$ and $ABCF$ with an intersection of $ABC$ since it is a $K_3$, but cut-vertices and cut sets of cardinality 2 joined by an edge are the most useful. I added in how to use it for $G/AE$.
May
21
revised Help me calculating chromatic polynomial of this subgraph
added 375 characters in body