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Eco models > Chapter 1 > Flashcards

Chapter 1 Flashcards

1
Q

What is a system?

A

Limited part of reality that contains interrelated elements. The totality of relations within the system is called “system structure”.

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2
Q

What is a model?

A

A simplified representation of a system.

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3
Q

How does the modelling scheme go?

A

Reality - System -Model

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4
Q

What are the two basic assumptions of a model (dynamic)?

A
  1. The state of a system can be always quantified.
  2. Changes in the states (rates) can be described by mathematical equations.
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5
Q

What is the dimension (unit) of 1. State variables, 2. Rate variables, 3. Driving variables?

A
  1. state = amount
  2. rate = amount/time
  3. driving = not known beforehand
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6
Q

What is a simulation?

A
  1. The building of a model
  2. and the study of the model behaviour in respect to its system
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7
Q

What are the type of models? (in respect to time and characteristics)

A

Time:
Static
Dynamic
Characteristic:
Descriptive
Explanatory

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8
Q

What is a static model?

A

A model that does not include the time dimension.

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9
Q

What is a dynamic model?

A

A model that includes the time dimension.

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10
Q

What is a descriptive model?

A

A model that shows the
existence of relations
between the elements of a
system without any
explanation.

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11
Q

What is an explanatory model?

A

A model that explains the
behaviour of a system at
an upper integration level
by integrating processes of
a lower integration level

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12
Q

What is an important thing to keep in mind when thinking about a system’s boundaries?

A

Choose a boundary such that the environment might influence the system, but that the system
does not affect the environment significantly.

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13
Q

What is a state variable?

A

An element of a system structure that represents a quantity; this quantity should
be additive.

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14
Q

What is a rate variable?

A

Variable indicating the rate at which the
state variables change.

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15
Q

What is a parameter?

A

A variable with a value that does not
change during the simulation and is
provided beforehand.

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16
Q

What is a driving variable?

A

Characterization of the influence of
external actors on the system, which are not influenced by the processes within the
system.

17
Q

What is a variable of extension?

A

Variables represent an amount, meaning that they can be added or
subtracted

18
Q

What is a variable of intensity?

A

Variables of intensity cannot be added or subtracted. Examples are temperatures and concentrations. But these variables of intensity can be calculated from variables of extension.

19
Q

What are the basic rules of Unit Analysis?

A
  1. both sides of the equal sign should have the same units.
  2. ONLY values with the same units can be added/subtracted.
  3. Log and exponentials
    OR
  4. The terms that are added, subtracted or
    compared must have the same dimensions or units. So both sides operators (=, +, -, <, > or combinations of these must have the same dimension and unit.
  5. The dimensions and units of the expressions on both sides of the equal sign should be identical.
  6. In multiplication reciprocal dimensions cancel out.
    In division identical dimensions cancel out (a division is the same as a multiplication with its reciprocal).
  7. The arguments of exponentials, logarithms and angles should be dimensionless.
20
Q

What are the theoretical phases of systems analysis?

A
  1. Concept model formulation
  2. Quantitative model specification
  3. Model evaluation
  4. Model use
21
Q

What are relational diagrams?

A

Diagrammatical representation of system’s components and their relationships, which collectively form our conceptual model, using symbols that indicate the specific nature of the relationships.

22
Q

Objects in relational diagrams (most important: squares etc)

A

State - rectangle
Rate - valve
Parameters - line with circle in middle
Auxiliary variable - circle
Influence - dotted line
source - cloud

23
Q

What is feedback?

A

The influence of a state on its own rate of change.

24
Q

How can models be solved?

A

Analytically
Numerically

25
Q

What is the difference between analytical solutions and numerical solutions?

A
  1. Analytical solutions are only available for relatively simple problems (needs the primitive function for the determined integral).
  2. A model can be always solved numerically.
  3. Calculating a new state of the system
    * Integrate all derivatives in the model
26
Q

What is a time coefficient (tau)?

A

The time needed for a model to reach its equilibrium state when the rate is
kept constant.

27
Q

What is a time step (delta t)?

A

Instead of representing time continuously, models discretize time into intervals. The time step (Δt) determines the size of these intervals.

28
Q

What are the rules for choosing the correct time step (delta t)?

A
  1. Based on an analysis of the time coefficients (tau) within the system (rule of thumb)
  2. Time step should be small enough to track the dynamics of driving variables
  3. Time step should make sure that time-driven discontinuities will take place in the
    simulation
    A pragmatic approach to test the choice of the time step is the ‘trial and error’
    approach.
29
Q

What is the relationship between integration levels, characteristic times and generalisation potential?

A

High integration level (Vegetation) - Low Generalisation level - Large Characteristic time

Low integration level (molecule) - High Generalisation level - Small Characteristic time

30
Q

In a numerical solution, what does error depend on?

A
  1. Value of ∆𝑡 : the time-step (the higher the vale the higher the error)
  2. Choice of numeric integration method (Euler more basic than Runge Kutta 4th order)
  3. Processes in the system: characteristic time or time coefficient
31
Q

What is the equation for the time coefficient (tau)?

A

tau =|(State in equilibrium (S_eq) - State at time t (S_t))/rate of change of state (dS_t/dt)|

32
Q

Systematic Problem Approach

A
  1. Think of the question clearly, reformulate it
  2. Rewrite information that are given
  3. design problem solving strategy: see what info is missing (rewrite equations)
  4. Derive information that is lacking by external source.
  5. Use info to answer original question.
33
Q

How can we determine the usefulness of models?

A
  1. Are they testable?
    a. yes - Verifiable models (repeatable systems or recurring) (allows their predictions to be tested and validated against observed data)
    b. no - Speculative models (used to explore potential scenarios, generate hypotheses, or simulate systems where empirical data may be limited or uncertain)
  2. How general are they (Generality)?
    a. Spatial/temporal limitations taken into consideration?
    b. Are all relevant processes included?
34
Q
A

Eco models (9 decks)

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