The State of a system

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Systems modelling concepts
System modelling concepts
What is a modelling?
Model classification
Dynamical Systems
System analysis-System dynamics and thinking
Introduction to course litterature
What is modelling?
Mind modelling
So, thinking is modelling
If the thought is clear and
can be communicated, then
we can always model it.
Modelling is to get
an idea of how
things are or work.
What is a model?
A model
- a replica
- an ideal
- to display
Dictionary
- a simplified representation
of the world around us or a
material, conceptual or formal
representation
Book: section1.2
Semi-distributed model
HBV
SMHI, developed by Sten
Bergström and colleagues.
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p  p0 EXP 
R
T
a
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z 

A model is:
- A model is any understanding which is used to
reach a conclusion or a solution
-There are no computer models, these are mere
mechanical and mathematical translations of
mental models
-If a model is ’wrong’, then the underlying
understanding is wrong
The value of models:
-Forces us to examine a system carefully and
define key variables, relationships,
processes, structures and scales
-Helps us to understand the functioning
-Enables us to extrapolate in
– scale and space
- future (forecasts)
- past(hindcast)
-Enables us to interpolate
-Allows us to obtain or infer information
about unmeasurable variables
Models have the potential to:
-Quantify expected results
-Compare the results of two alternative theories
-Describe the effect of complex factors, such as
random variation in inputs
-Explain how the underlaying processes contribute to
the result
-Extraplota results to other situations
-Predict future events
-Translate our science into a form that can be easily
used by non-experts
Book: section 1.3
Types of models
Increasing abstraction
Models
Scale
Hardware
Analogue
Conceptuel
Deterministic
Matematical
Probabilistic
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p  p0 EXP 
 RaT
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Example; light absorbtion in a canopy
Model classification
Question
Hypothesis
Output
Input
Scope
Application
Output
Qualitative / quanitiative?
Deterministic / stochastic?
Input
Static / dynamic?
Scope
Descriptive / predictive?
Book: section 1.4
Application
Functional / mechanistic?
Model classification
Question
Hypothesis
Output
Input
Scope
Application
Output
Qualitative / quanitiative?
Deterministic / stochastic?
Input
Static / dynamic?
Scope
Descriptive / predictive?
Application
Functional / mechanistic?
Discuss examples:
1. A stylist use a model to suggest what colours dress you best
2. A weather forecast model
3. Betsson (a betting company) needs a model to set odds for which song
will win the Eurovision song contest
Dynamical systems
Systems in the society
Football formation system
What do they have in common?
Education system
Transport system
Defence system
Systems in
nature:
Isolated system
Closed system
Energy
Isolated system: no exchange with its
environment
Closed systems: only exchange of energy
Open system
Open systems: exchange of both energy and
matter with its surroundings
Matter
Systems
 Representation of a part of reality that is bounded in its
surrounding
 Consist of a number of elements (entities, components)
 The state of the elements effects each other, which makes
the system functioning (or work)
Simple
Complicated
Simple representation of a
complicated system
Ecosystem:
An ecosystem is a biotic and functional system or unit,
which is able to sustain life and includes all biological and
non-biological variables in that unit. Spatial and temporal
scales are not specified a priori, but are entirely based upon
objectives of the ecosystem study
(Jorgensen & Bendoricchio, 2001)
A system:
A system is a group of independent but interelated
elements comprising a unified whole
But:
The properties of the whole can only be understood
through the interaction and the relationships
among the parts within the system
+
For example: a forest stand
In isolation the parts can not be
considered as a forest. It is the
interaction between the parts that
makes it a forest
=
+
A system element:
can be specified by its properties (a tree:
height, leaf area)
The State of a system:
the value of relevant properties at a moment
in time
Process:
a (time dependent) relation that changes the
state of a system
To summarize the characteristics of a system:
1. All descriptions or models of systems are to some extent
generalizations, abstractions or idealization of the real world.
2. Systems have some kind of structure or organization of its
objects and a boundary.
3. A system is functioning in some way
4 Because it is functioning, there are functional as well as
structural relationships between the objects in the structure.
5. The functioning implies some flow and transfer of material or
energy through the system
6. This means that there is a driving force, or a source of energy
that support the functioning, or drives the system
The discipline of System dynamics and system thinking
System dynamics = analysis and understanding of the behavior
of systems:
a methodology for studying and managing complex systems or
any feedback system. It uses simulation (computer) models.
It is seeing the whole (holism) versus Reductionism
System thinking as a discipline
for seeing systems as a wholes, it counteracts
reductionism looks at relationships between system
elements
looks at dynamic changes
It focus on how the system ’works’: the processes and interrelations – as a mean to understand the system
System dynamics
Originated in 1960’s from work of Jay Forrester et al of
Massachusetts Institute of Technology
’Industrial Dynamics’ (1961), ’Urban dynamics’ (1969) and ’World
dynamics’ (1971)
System dynamics
Other examples
Limits to Growt
Donella L. Meadows et al, 1972 (World3model)
Club of Rome (1968)
http://www.clubofrome.org/
Our common future (1987)
United Nations World Commission on
Environment and Development, headed by
Gro Harlem Brundtland, Previous Prime
Minister of Norway
Informal association of
leading long-term thinkers
contributing in a systematic
interdisciplinary and holistic
manner to a better world
It targets multilateralism and
interdependence of nations in
the search for a sustainable
development path, and aims to
discuss the environment and
development as one single issue.
Basic elements in system
modelling
Parameters
Constants
Variables
Flows
Stocks
Processes
Stages in making a model
Answer
Research
question
Evaluation
Picture
Measurements
Hypothesis &
assumptions
Mathematical
model
Book: section 1.6
Litterature
Smith & Smith: Environmental Modelling
www.oxfordtextbooks.co.uk/orc/smith_smith/
1: Introduction (22 Jan)
2: Model Development (30 Jan)
3: Model Evaluation (8 Feb)
4: Application of Models (15 Feb)
Litterature
Smith & Smith: Environmental Modelling
www.oxfordtextbooks.co.uk/orc/smith_smith/

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