Graph: Euler Path and Euler
Circuit
By Prof. Liwayway Memije-Cruz
Konigsberg Seven Bridges
A graph is a diagram displaying data; showing
the relationship between two or more
quantities, measurements or indicative numbers
that may or may not have a specific
mathematical formula relating them to each
other.
What is a Graph?
acollection of pointscalled verticesor nodes, and
connecting segmentscalled edges.
sometimestheedgesaregiven orientationsand
arerepresented by arrowsor aregiven values
(weights).
theposition of thevertices, thelengthsof the
edges, and theshapeof theedgesdo not matter in
agraph. What welook at isthenumber of
verticesand which of them arejoined by edges.
EXAMPLESOF GRAPHS
The graph
indicates the
social network
of neurological
patients.
Molecular Structure
Computer Network
Judicial
System
CONSTRUCTING A GRAPH
Thefollowing tablelistsfivestudentsat auniversity.
An “X” indicatesthat thetwo studentsparticipatein
thesamestudy group thissemester.
Joshua Diego Butch Lianne Aby
Joshua --- X X X
Diego X --- X X
Butch X X --- X
Lianne X ---
Aby X X ---
Draw a graph that represents this
information where each vertex
represents a student and an edge
connects two vertices if the
corresponding students study together.
Simple Graph
also called astrict graph (Tutte1998, p. 2), isan unweighted,
undirected graph containing no graph loopsor multipleedges
(Gibbons1985, p. 2; West 2000, p. 2; Bronshtein and
Semendyayev 2004, p. 346). A simplegraph may beeither
connected or disconnected.
theunqualified term "graph" usually refersto asimplegraph. A
simplegraph with multipleedgesissometimescalled a
multigraph (Skiena1990, p. 89).
A graph isconnected if thereisapath
connecting all thevertices.
Two verticesareadjacent if thereisan edge
joining them.
If every pair of verticesof agraph are
adjacent, thegraph iscomplete. A
completegraph with n verticesisdenoted by
Kn.
Thedegreeof avertex isthenumber of edges
attached to it.
CompleteGraph
A completegraph isagraph in which each pair of graph
verticesisconnected by an edge. Thecompletegraph with
graph verticesisdenoted and has(thetriangular numbers)
undirected edges, whereisabinomial coefficient.
sometimescalled universal graphs.
https://www.youtube.com/watch?
v=Kwj5sdF8b18
Euler Path
 apath that uses
every edgeof a
graph exactly once.
 If apath beginsand
endswith thesame
vertex, it isaclosed
path or a
circuit/cycle.
 An Euler path starts
and endsat different
vertices.
Leonard Euler
A Swissmathematician and
physicist, oneof thefoundersof
puremathematics.
Henot only madedecisiveand
formativecontributionsto the
subjectsof geometry, calculus,
mechanics, and number theory
but also developed methodsfor
solving problemsin
observational astronomy and
demonstrated useful applications
of mathematicsin technology
and public affairs.
Examples of Euler Circuits
isacircuit that
usesevery edgeof
agraph exactly
once
aEuler circuit
startsand endsat
thedifferent
vertices.
Thenumber of edgesthat meet at avertex iscalled
thedegreeof avertex.
Eulerian Graph Theorem
A connected graph isEulerian if and
only if each vertex of thegraph isof
even degree.
Eulerian Graph Theorem only
guaranteesthat if thedegreesof all the
verticesin agraph areeven,
an Euler circuit exists, but it doesnot
tell ushow to find one.
Determinewhether thegraph below isEulerian. If it is, find
an Euler circuit. If it isnot, explain why.
Determinewhether thefollowing graph isEulerian. If it
is, find an Eulerian circuit. If it isnot, can you find an
Euler path?
Euler Path Theorem
• A connected graph containsan Euler path
if and only if thegraph hastwo verticesof
odd degreewith all other verticesof even
degree.
• Every Euler path must start at oneof the
verticesof odd degreeand end at theother.
https://www.youtube.com/watch?v=AwsMTEl79wI
Application of Euler Path Theorem
Below isthemap of all the
trailsin anational park.
A biker would liketo
traverseall thetrailsexactly
once.
Isit possiblefor thebiker to
plan atrip that traversesall
thetrailsexactly once?
Isit possiblefor him to
traverseall thetrailsand
return to
thestarting point without
repeating any trail in the
trip?
References:
http://mathworld.wolfram.com/Graph.html
https://study.com/academy/lesson/mathematical-models-of-euler
https://www.britannica.com/biography/Leonhard-Euler
https://www.maa.org/press/periodicals/convergence/leonard-eule
Mathematicsof Graphsby Ethel CecilleM. Baltazar

Graph: Euler path and Euler circuit

  • 1.
    Graph: Euler Pathand Euler Circuit By Prof. Liwayway Memije-Cruz
  • 2.
  • 3.
    A graph isa diagram displaying data; showing the relationship between two or more quantities, measurements or indicative numbers that may or may not have a specific mathematical formula relating them to each other.
  • 4.
    What is aGraph? acollection of pointscalled verticesor nodes, and connecting segmentscalled edges. sometimestheedgesaregiven orientationsand arerepresented by arrowsor aregiven values (weights). theposition of thevertices, thelengthsof the edges, and theshapeof theedgesdo not matter in agraph. What welook at isthenumber of verticesand which of them arejoined by edges.
  • 5.
  • 6.
    The graph indicates the socialnetwork of neurological patients.
  • 7.
  • 8.
  • 9.
  • 10.
  • 11.
    Thefollowing tablelistsfivestudentsat auniversity. An“X” indicatesthat thetwo studentsparticipatein thesamestudy group thissemester. Joshua Diego Butch Lianne Aby Joshua --- X X X Diego X --- X X Butch X X --- X Lianne X --- Aby X X ---
  • 12.
    Draw a graphthat represents this information where each vertex represents a student and an edge connects two vertices if the corresponding students study together.
  • 14.
    Simple Graph also calledastrict graph (Tutte1998, p. 2), isan unweighted, undirected graph containing no graph loopsor multipleedges (Gibbons1985, p. 2; West 2000, p. 2; Bronshtein and Semendyayev 2004, p. 346). A simplegraph may beeither connected or disconnected. theunqualified term "graph" usually refersto asimplegraph. A simplegraph with multipleedgesissometimescalled a multigraph (Skiena1990, p. 89).
  • 15.
    A graph isconnectedif thereisapath connecting all thevertices. Two verticesareadjacent if thereisan edge joining them. If every pair of verticesof agraph are adjacent, thegraph iscomplete. A completegraph with n verticesisdenoted by Kn. Thedegreeof avertex isthenumber of edges attached to it.
  • 16.
    CompleteGraph A completegraph isagraphin which each pair of graph verticesisconnected by an edge. Thecompletegraph with graph verticesisdenoted and has(thetriangular numbers) undirected edges, whereisabinomial coefficient. sometimescalled universal graphs.
  • 17.
  • 18.
    Euler Path  apaththat uses every edgeof a graph exactly once.  If apath beginsand endswith thesame vertex, it isaclosed path or a circuit/cycle.  An Euler path starts and endsat different vertices.
  • 19.
    Leonard Euler A Swissmathematicianand physicist, oneof thefoundersof puremathematics. Henot only madedecisiveand formativecontributionsto the subjectsof geometry, calculus, mechanics, and number theory but also developed methodsfor solving problemsin observational astronomy and demonstrated useful applications of mathematicsin technology and public affairs.
  • 20.
    Examples of EulerCircuits isacircuit that usesevery edgeof agraph exactly once aEuler circuit startsand endsat thedifferent vertices.
  • 21.
    Thenumber of edgesthatmeet at avertex iscalled thedegreeof avertex.
  • 22.
    Eulerian Graph Theorem Aconnected graph isEulerian if and only if each vertex of thegraph isof even degree. Eulerian Graph Theorem only guaranteesthat if thedegreesof all the verticesin agraph areeven, an Euler circuit exists, but it doesnot tell ushow to find one.
  • 23.
    Determinewhether thegraph belowisEulerian. If it is, find an Euler circuit. If it isnot, explain why.
  • 24.
    Determinewhether thefollowing graphisEulerian. If it is, find an Eulerian circuit. If it isnot, can you find an Euler path?
  • 25.
    Euler Path Theorem •A connected graph containsan Euler path if and only if thegraph hastwo verticesof odd degreewith all other verticesof even degree. • Every Euler path must start at oneof the verticesof odd degreeand end at theother.
  • 26.
  • 27.
    Application of EulerPath Theorem Below isthemap of all the trailsin anational park. A biker would liketo traverseall thetrailsexactly once. Isit possiblefor thebiker to plan atrip that traversesall thetrailsexactly once? Isit possiblefor him to traverseall thetrailsand return to thestarting point without repeating any trail in the trip?
  • 28.