lec 2 systems thinking

system

set of interacting or interdependent components forming an integrated whole/collective entity

elements/components

entities, state variables, or reservoirs

linkages/couplings

relationships, connections or flows linking elements

boundaries

where the system ends (earth for the hydrological cycle example)

open system

porous boundary allowing inputs and outputs

closed system

non-porous boundary, rarer than opens

simple system

few, linear relationships with predictable outcomes

complicated systems

many branching linear relationships, a few loops, outcomes can be carefully predicted

complex systems

many nonlinear branching relationships and loops, resilient but surprises occur, has subsystems

qualitative systems

deal with linked concepts e.g. social groups, circumstances

quantitative systems

deal with linked measurable quantities of components and transfers between them

element dynamics

change in element's state depends on balance between input and output

component sources (I)

inputs/net inflows, units per unit time

component sinks (O)

outputs/net outlows, units per unit time

element (E)

quantity in a reservoir, units of stuff

dE/dt =

I - O

system is in steady state if

I = O for elements such that E will not changet

transient state

if there is any difference in I and O

systems easier to understand in steady state because

we can often find time windows to make that assumption and don't have to worry about changes in I or O