System perspective

1. What is a system?

flowchart LR
subgraph g[sys.]
processor[processor]
end
x((input)) --> processor --> y((output))

Fig.1. A system

System is something that takes given inputs, process them and generate intended outputs.

Discussion Give system examples.

• Engineering systems
• Computer systems
• Biological systems
• Mathematical systems

Discussion What are input/output and processor? Use some practical systems to explain your idea.

Tips:

• A system is composed of three parts: inputs, outputs, and processor.
• To define a system, all three parts have to be carefully defined.
• The processor have some other names in different fields, e.g., operator, machine, etc.
• A system may have multiple inputs or multiple outputs.

flowchart LR
subgraph g1[A system with multiple inputs]
processor1[processor]
end
x1((input I)) -->processor1 --> y((output))
x2((input II)) -->processor1
subgraph g2[A system with multiple outputs]
processor2[processor]
end
x3((input I)) -->processor2 --> y1((output I))
processor2 --> y2((output II))

Fig.2. Systems with multiple inputs or outputs

Question How does the term function in math differ from the same term in computer science?

3. Complex systems

Simple systems can be connected in different ways to compose a complex system.

Discussion How could systems be connected? Provide examples.

flowchart LR
subgraph s1[sys. I]
 p1[processor I]
 end
x((input)) --> p1 --> y((output of sys. I))
subgraph s2[sys. II]
p2(processor II)
end
y --as the input--> p2 --> z((output of sys. II))
style y fill:#f9f

Fig.3. Two sequentially-connected systems

System network

flowchart LR
subgraph sys1[system I]
operator1(function I)
end
subgraph sys2[system II]
operator2(function II)
end
subgraph sys3[system III]
operator3(function III)
end
subgraph sys4[system IV]
operator4(function IV)
end
x((input I)) --> operator1 -- output I --> operator3;
y((input II)) --> operator2 -- output II --> operator3;
operator3 -- output III --> operator4 --> z((output))

Fig.4. A network of systems