---parityerror.nlogo

NETLOGO

; Parity Error Detection Simulation 
; written by Teresa Carrigan, 2004 


globals [ from-number from-string number-of-digits start-x myDigits praise digits1 save-base base step error-detected?] 
breeds [ digit arrow ones ] 
arrow-own [ state ]
patches-own [ name ]


; runs the program when it is first loaded
to startup
  setup
end

; initializes variables
to setup
  locals [here-x current n]
  ca
  set praise ["Awesome!" "You got it!" "Right!" "Correct!" "Perfect!" "Bravo!" "Splendid!"]
  set digits1 [ "0" "1" ]
  set base 2
  set save-base base
  set myDigits []  
  set n 0
  set start-x 9
  set here-x 7
  set current 1
  set n 0
  
  repeat 2 [
        set myDigits lput ( item n digits1 ) myDigits
        set n (n + 1)
    ]  
  set n 1
  
  set number-of-digits 8
  ;  initialize binary number
  set from-number ""
  repeat number-of-digits
    [  set from-number (word from-number (random-one-of myDigits))
    ]
  
; create explanation bar at bottom
  ask patches with [ pycor < -3 ]
    [set pcolor blue]
  ask patch-at 6 -4
    [ set plabel  (word  add-space from-number " was sent using " parity " parity.")
      set plabel-color white
      set name 1
    ]
  ask patch-at 6 -5
    [
      set plabel-color white
      set plabel "Do we detect an error in transmission?"
      set name 2
    ]
  set step 1

  setup-bits from-number
  setup-arrow

end

to step1
  explain 1 "Ignore the 0 bits."
  explain 2 ""
  
  ask digit with [ label = "1 " ]
    [  hatch 1
          [  set breed ones
             set shape "circle"
             set color yellow
             set size 2
             set label-color black
          ]
    ]
  ask ones
    [ set heading 180 
      repeat 4
          [ fd 0.5
            wait slow-motion
          ]
    ]
  set step step + 1
end

to step2
  ifelse count ones with [ color = yellow ] = 0
    [ set step step + 1]
    [   ask arrow 
        [  showturtle
           ifelse any? other-ones-here
             [  ask other-ones-here
                   [ set color red ]
                if count ones with [color = red] = 2
                  [ explain 2 "Dropping a pair of ones." 
                    ask ones with [color = red]
                        [ die ]
                    wait slow-motion
                  ]
                fd 1
             ]
             [  explain 2 ""
                fd 1
             ]
        ]      
    ]
end
  
;  read the digits, storing it as a string
; adds a space in the number so it can be read easier
to-report add-space [ number ]
  locals [ save k ]
  set save ""
  set k 0
  while [ (length number) > 0 ]
    [
      set save (word last number save )
      set number butlast number
      set k (k + 1)
      if (k = 4) and (length number > 0)
        [ set save (word " " save )
          set k 0
        ]
    ]
  set number save  
  report number
end



; this is for the bottom explanation
to explain [ which what ]
  ask patches with [ name = which ]
    [ set plabel what ]
end

; setup the red arrow
to setup-arrow
  locals [here-y ]
  ask random-one-of digit [ set here-y ycor ]
  
  ;  create red arrow
  cct-arrow 1 [
    hideturtle
    setxy start-x ( here-y - 2)
    set heading -90
    set color red
    set shape "arrow"
    set size 2
    set state 0
  ]
end

; setup the bits
to setup-bits [ unsigned ]
  locals [ here-x here-y]
  set here-x ( start-x - 2)
  set here-y 2
  repeat number-of-digits
    [
      cct-digit 1
      [ 
        setxy here-x here-y
        set shape "circle"
        set color white
        set size 2
        set label-color black
        set label (word (last unsigned)  " ")
      ] ; end cct digits
      set unsigned but-last unsigned
      set here-x (here-x - 2)   
      wait slow-motion
    ]
  
end


to step3
  locals [ here-parity ]
  ask arrow
    [ hideturtle ]
  ifelse count ones = 0
    [ set here-parity "even" 
      explain 1 "No ones left, so parity is currently even."
    ]
    [ set here-parity "odd" 
      explain 1 "A one left, so parity is currently odd."
    ]
  explain 2 ""
  wait slow-motion
  set step step + 1
end

to step4
  locals [ here-parity ]
  ifelse count ones = 0
    [ set here-parity "even" 
    ]
    [ set here-parity "odd" 
      ask ones [ die ]
    ]
  ifelse here-parity = parity
    [ explain 2 "NO error is detected." 
      set error-detected? false
    ]
    [ explain 2 "YES an error is detected."
      set error-detected? true
    ]
  wait slow-motion
  set step  10
end


; creates a random quiz quesiton and praise if it is right and says its wrong if it is
to ask-question
  locals [ guess save-slow target line]
  set line (word  add-space from-number " was sent using " parity " parity.\n")
  set line (word line "Do we detect an error in transmission?")
  set guess user-yes-or-no? line
  set save-slow slow-motion
  set slow-motion 0
  while [ step < 10 ]
      [  go  ]
  set slow-motion save-slow
  set target error-detected?
  ifelse guess = target
    [  user-message random-one-of praise ]
    [  set line  "I'm sorry, but "
       ifelse target
         [ set line line + "YES an error was detected." ]
         [ set line line + "NO error was detected." ]
       user-message line
    ]
end

; calls the quiz when the button is pressed
to quiz
  locals [ save-slow ]
  set save-slow slow-motion
  set slow-motion 0
  set parity random-one-of [ "even" "odd" ]
  without-interruption [setup ]
  wait .5
  ask-question
  set slow-motion save-slow
end


; flips the digits (called by the invert procedure)
to flip
  if any? other-digit-here
    [
      ask other-digit-here
        [  set color yellow
            ifelse first label = "0"
              [  set label "1 " ]
              [  set label "0 " ]
        ]
    ]
end


;  do whatever step comes next, then wait until user wants to continue
to one-step
  locals [ which ]
  if step < 10
    [  set which (word "step" step)
       run which
    ]
end


; this is the go button, that when pressed, goes through the entire simulation
to go
  ifelse  step < 10 
    [  one-step
       wait slow-motion
    ]
    [  stop
    ]
end

to show-again
  locals [here-x current n]
  set start-x 9
  set here-x 7
  set current 1
  set n 1
  
  set number-of-digits 8
  
  ask turtles [die]
  ask patches [ set plabel "" ]
  explain 1 (word  add-space from-number " was sent using " parity " parity.")
  explain 2 "Do we detect an error in transmission?"

  set step 1

  setup-bits from-number
  setup-arrow
end

; *** NetLogo Model Copyright Notice ***
;
; Copyright 2004 by Teresa W. Carrigan.  All rights reserved.
;
; Permission to use, modify or redistribute this model is hereby granted,
; provided that both of the following requirements are followed:
; a) this copyright notice is included.
; b) this model will not be redistributed for profit without permission
;    from Teresa W. Carrigan.
; Contact Teresa W. Carrigan for appropriate licenses for redistribution 
; for profit.
;
; To refer to this model in academic publications, please use:
; Carrigan, T. (2004).  Parity Error Detection Simulation
; Blackburn College, Carlinville, IL.
;
; In other publications, please use:
; Copyright 2004 by Teresa W. Carrigan.  All rights reserved.  
;
; *** End of NetLogo Model Copyright Notice ***
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CC-WINDOW
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Command Center

BUTTON
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NIL
setup
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OBSERVER
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SLIDER
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slow-motion
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BUTTON
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step
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OBSERVER
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BUTTON
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go
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1
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OBSERVER
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CHOICE
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parity
parity
"even" "odd"
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BUTTON
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NIL
quiz
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OBSERVER
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BUTTON
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NIL
show-again
NIL
1
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OBSERVER
T

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WHAT IS IT?
-----------
This model demonstrates the detection of single bit errors in bit patterns stored using either even or odd parity. 

HOW IT WORKS
------------
First, a random eight-bit binary number is generated.  Any bit that is a 1 will hatch a yellow copy of itself.  The red arrow then discards pairs of yellow 1 bits.  If there are no yellow bits left over, the current parity is even; if there is a bit left over, the current parity is odd.

Next, the current parity is compared to the parity used when the bit pattern was stored.  If they match, then no error is detected.  If they do not match, then an error was detected.


HOW TO USE IT
-------------
The setup button generates a random eight-bit binary number.

The step button demonstrates the next step, and then stops so you can take notes.  This is useful when you are first learning the method.

The go button does every remaining step, at a speed determined by the slow-motion slider.  This is useful when you do not need to take notes between each step.

The show-again button starts the exact problem from the beginning.  You may then click either the step button or the go button to see the same demonstration.

The quiz button will generate a random bit pattern and ask the user if an error was detected, using a specified parity.

The slow-motion slider is an easy way to adjust the speed of the display.  Set it to zero if you want to show the final result as quickly as possible.  0.5 is a good setting for most purposes.

The parity choice box specifies whether even or odd parity will be demonstrated.


THINGS TO NOTICE
----------------
Any bits that are zero are always ignored.  The number of bits does not change the parity either.

The receiver must know not only whether the message was sent using even or odd parity, but also whether the parity bit is the first or last bit.  This means that even if no error is detected, we cannot determine the data bits, because we are not told whether the parity bit was first or last.

When an error is detected, there is no way to fix the error, other than to ask for the message to be sent again.

THINGS TO TRY
-------------
Set slow-motion to 0.5, click setup, and then click go.

Set the parity to a type you wish to drill, and click setup.  Work each step by hand, and then click the step button to check your answer.

EXTENDING THE MODEL
-------------------
Allow the user to input the starting bit pattern.


NETLOGO FEATURES
----------------
one-step uses the NetLogo run command combined with a global integer variable step to run the next step, without needing nested ifelse blocks. 

without-interruption runs all the commands in the block without allowing other agents to "interrupt". That is, other agents are put "on hold" and do not execute any commands until the commands in the block are finished. 


RELATED MODELS
--------------
Parity Simulation


CREDITS AND REFERENCES
----------------------
This model was written by Teresa W. Carrigan, 2004.  

Permission to use, modify or redistribute this model is hereby granted,
provided that both of the following requirements are followed:
	a) this copyright notice is included.
	b) this model will not be redistributed for profit without permission
	   from Teresa W. Carrigan.
Contact Teresa W. Carrigan for appropriate licenses for redistribution 
for profit.

To refer to this model in academic publications, please use: 
Carrigan, T. (2004). Parity Error Detection Simulation
Blackburn College, Carlinville, IL.

In other publications, please use: 
Copyright 2004 by Teresa W. Carrigan.  All rights reserved.  

FOR MORE INFORMATION
--------------------
For more information on parity, see:
Null, L. and Lobur, J. "Essentials of Computer Organization and Architecture", First Edition. Jones and Bartlett. page 65.
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arrow
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box
true
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circle
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NetLogo 2.0.1
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