Discrete Event Simulation
Dr Tracey England
Taxonomy of OR methods
OR Methods
Methods to calculate
an attribute of a
system
“Soft” methods
Methods to help
structure illstructured problem
situations
Methods for more
structured problems
-parameters difficult
to quantify
Deterministic
methods
Methods to replicate
or forecast system
behaviour
Optimization
methods
Deterministic
replication methods
Optimization of
deterministic
systems
Statistical methods
Stochastic replication
methods
Optimization of
stochastic systems
Static Monte Carlo
simulation methods
Complexity
understanding
methods
Stochastic methods
Probabilistic methods
Williams, T (2008) Management Science in Practice, Wiley. p.101
Logic methods
What is Discrete Event Simulation?
• Models a system as a sequence of discrete events in
time.
• Each event occurs at a certain instant in time.
• The simulation keeps track of the time and the next
event in the list to be triggered.
• May undertake several runs of the model and then
look at the results, e.g. mean waiting time,
utilisation.
DES Software
• Open source
– SIMPY: python based software
• Commercial packages
– SIMUL8
– ANYLOGIC
Where I have used DES
• Trauma and Orthopaedic Unit, Royal Gwent Hospital
• Glaucoma, Lucentis, Cornea and paediatric
outpatient clinics, Royal Gwent Hospital
• ABMU Out of hours
• NHS Direct Wales
Why it has been useful
• Visual representation that aids discussion between
the different people involved.
• Use of “what-if” scenarios to evaluate different
options.
• To “try before you buy” – allows you to model
systems before they are built for real
Resources
• Staff
• Computers and equipment
• Rooms
Timings
Outputs
DES in Ophthalmology
NHS Direct Screenshot