The Edexcel D1 (18/05/12 - AM) Revision Thread

OP

Fairly certain you do not need to know about Hamilton. Will try to remember to upload the MS requested tomorrow.

OP

I have uploaded them

June 2009 Markscheme is being an absolute bitch to find

Reply 23

Original post by Arsey

Fairly certain you do not need to know about Hamilton. Will try to remember to upload the MS requested tomorrow.

That's a good reassurance :biggrin:

Reply 24

Estelle123

2

Original post by Arsey

I have uploaded them

thank you so much!

Reply 25

OP

Definitions for the D1 Exam (and what they really mean!)

Graphs
A graph G consists of points (vertices or nodes) which are connected by lines (edges or arcs). A graph is just some points joined together with lines.

A subgraph of G is a graph, each of whose vertices belongs to G and each of whose edges belongs to G. A subgraph is just part of a bigger graph.

If a graph has a number associated with each edge (usually called its weight) then the graph is called a weighted graph or network. A weighted graph is one with values, eg distance, assigned to the edges.

The degree or valency of a vertex is the number of edges incident to it. A vertex is odd (even) if it has odd (even) degree. The degree of a vertex is how many edges go into it.

A path is a finite sequence of edges, such that the end vertex of one edge in the sequence is the start vertex of the next, and in which no vertex appears more than once. A path describes a ‘journey’ around a graph, where no vertex is visited more than once.

A walk is a path where you may visit vertices more than once.

A cycle (circuit) is a closed path, i.e. the end vertex of the last edge is the start vertex of the first edge.

Two vertices are connected if there is a path between them. A graph is connected if all its vertices are connected. Two vertices are connected if you can walk along edges from one to the othe, in a connected graph all vertices are connected.

If the edges of a graph have a direction associated with them they are known as directed edges and the graph is known as a digraph. A digraph will have arrows on the edges.

A tree is a connected graph with no cycles.

A spanning tree of a graph G is a subgraph which includes all the vertices of G and is also a tree.

A minimum spanning tree (MST) is a spanning tree such that the total length of its arcs is as small as possible. (MST is sometimes called a minimum connector.)

A graph in which each of the n vertices is connected to every other vertex is called a complete graph. In a complete graph every vertex is directly connected to every other edge.

Matchings

A bipartite graph consists of two sets of vertices X and Y. The edges only join vertices in X to vertices in Y, not vertices within a set. (If there are r vertices in X and s vertices in Y then this graph is Kr,s.) A bipartite graph has two sets of nodes. Nodes of one set can only be matched to nodes of the other set.

A matching is the pairing of some or all of the elements of one set, X, with elements of a second set, Y. If every member of X is paired with a member of Y the matching is said to be a complete matching. In a matching some of one set are joined to the other. In a complete matching they’re all joined.

An Alternating Path starts at an unconnected vertex in one set and ends at an unconnected vertex in the other set. Edges alternate between those ‘not in’ and ‘in’ the initial matching.

Reply 26

OP

Original post by Arsey

Fairly certain you do not need to know about Hamilton. Will try to remember to upload the MS requested tomorrow.

Gibbo says that Hamilton is only needed in D2, even then you don't need the definition.

Reply 27

Original post by Arsey

Gibbo says that Hamilton is only needed in D2, even then you don't need the definition.

Thanks,

Also, on June 09, Q7e, I got the points for the optimal number of large and small baskets as

250/7 and 20

Now the problem is 250/7 is 35.7... but the MS have rounded it down to 35 whereas I have rounded it up to 36, therefore, i don't get the correct anser.

Why do they round it down? Is it because it's optimal? What does optimal even mean?

Reply 28

WaNaBe

1

Original post by This Honest

Thanks,

Also, on June 09, Q7e, I got the points for the optimal number of large and small baskets as

250/7 and 20

Now the problem is 250/7 is 35.7... but the MS have rounded it down to 35 whereas I have rounded it up to 36, therefore, i don't get the correct anser.

Why do they round it down? Is it because it's optimal? What does optimal even mean?

I haven't done the question, but I'd assume that they have rounded down because 35 would be within the feasible region and that 36 wouldn't be.

I believe that optimal just means the best value you can have that is feasible (In the area that isn't shaded).

Reply 29

Original post by WaNaBe

I haven't done the question, but I'd assume that they have rounded down because 35 would be within the feasible region and that 36 wouldn't be.

I believe that optimal just means the best value you can have that is feasible (In the area that isn't shaded).

I think 36 is in my region?
hmm perhaps :holmes:

Reply 30

ps3g4m3r

Original post by This Honest

I think 36 is in my region?
hmm perhaps :holmes:

Graphs are subject to human error, whack 36 into the inequalities and it will probably not satisfy one of them if its not in the MS :wink:

Reply 31

Legendary

1

Can't wait to get this out of the way so I can do some real maths. :colone:

Reply 32

CharrrrxD

Hi
I always make stupid mistakes on D1 :frown:

Is there any way to stop this?
I know that sounds ridiculous but I always do the right thing but if you make one stupid mistake it all goes wrong and lose so many marks arghhhhh
Thanks anyone :smile:

Reply 33

Original post by CharrrrxD

Hi
I always make stupid mistakes on D1 :frown:

Is there any way to stop this?
I know that sounds ridiculous but I always do the right thing but if you make one stupid mistake it all goes wrong and lose so many marks arghhhhh
Thanks anyone :smile:

The only way is practise. I know it sucks but you need to be more careful and watch what you're writing and typing on your calculator.

Perhaps, speding more time on the topics that you are always making frequent mistakes on.

Reply 34

OP

Original post by This Honest

Thanks,

Also, on June 09, Q7e, I got the points for the optimal number of large and small baskets as

250/7 and 20

Now the problem is 250/7 is 35.7... but the MS have rounded it down to 35 whereas I have rounded it up to 36, therefore, i don't get the correct anser.

Why do they round it down? Is it because it's optimal? What does optimal even mean?

without checking it is probably because point rounded up would lie outside the feasible region.

Sub the values into the equations of the lines giving the optimal point to see if it holds, I doubt it will.

Reply 35