COP 3223H meeting -*- Outline -*-

* Modeling with Programs

** What programs do

    Imagine a program that flies an airplane (an autopilot)...
    
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           WHAT A PROGRAM DOES

How does a program control an airplane
(or a car, etc.)?

 environment                     environment
    |                                 ^ 
    v            [---------]          |
 sensors and --> [ Program ] ---> actuators
 input devices   [---------]      and output
                                   devices
     
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        This may look like a one time event, but it can be repeated
        over and over, e.g., every 0.1 second

        An interactive program just repeats this cycle with the user
        as part of the environment

        Q: What are some examples of sensors or input devices?
           for an airplane, things like: wind speed, position,
           altitude, ...
           In a smartphone, things like: position, presses on the
           screen (with their positions)
           On a laptop computer: keyboard, mouse (with positions),
                                 battery level...

        Q: What are some examples of actuators or output devices?
           for an airplane, things like: hydralauics that control flaps,
                                         flow of fuel to the engines, ...
           In a smartphone or laptop, things like: 
                    the display, the speakers,
                    a wireless connection to the internet
                    (you could think of a printer or a port connected
                     to it also as an output device)

*** The OS helps abstract away devices

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  FROM THE POINT OF VIEW OF THE PROGRAM

With the help of the Operating System (OS):

                [---------]          
 input data --> [ Program ] ---> output data
                [---------]     

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    The operating system allows us to make this abstraction,
    as it handles dealing with the devices at a low level

    The OS presents to the program data in a format it can understand
    (e.g., character strings)

*** Why we can model programs using simple inputs and outputs
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SOPHISTICATED DEVICE CONTROL ISN'T NEEDED

An old application: Artillery range finding

Problem: what angle to aim an artillery
    piece at to hit a certain target
    (at a given distance)?

Solution:

Some person tells the operator where
to shoot (the environment)

Some types into the computer the distance
(input).

The program does a calculation (using physics)

The program prints out the angle (output).

The operator adjusts the angle (actuator).
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   In this app the program substitutes for a table/book that gives angles

** The conclusion about modeling
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    THE CONCLUSION ABOUT MODELING

Abstractly every computer program
is "blind" but models the real world


 environment's               change to
 state                       environment
 (user's question)           (user's answer)
      |                          ^
      | encoding                 | interpretation
      v                          |
 representation -->[Program]--> output
 as input                    representation

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      The key idea is that the inputs and outputs of the program
      are not themselves reality, but *represent* reality.

      Inputs and outputs are always interpreted (given meaning) by the
      user or the environment.

      This leads us to looking at the data we can use in modeling...