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"{ Package: 'stx:libbasic2' }"
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Random subclass:#RandomLaggedFibonacci
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instanceVariableNames:'values drift'
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classVariableNames:''
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poolDictionaries:''
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category:'Magnitude-Numbers'
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!
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!RandomLaggedFibonacci class methodsFor:'documentation'!
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documentation
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"
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The lagged Fibonacci additive generator is described in
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TAOCP vol. 2 by Donald Knuth, with lags 83 and 258.
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"
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! !
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!RandomLaggedFibonacci methodsFor:'accessing'!
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drift
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^ drift
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!
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drift:something
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drift := something.
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!
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next
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| answer |
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answer := self nextValue.
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self increaseDrift.
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self values at: self drift put: answer.
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^ answer
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!
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nextValue
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| answer |
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answer := self smallLagValue - self largeLagValue.
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answer < 0.0 ifTrue: [answer := answer + 1.0].
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^ answer
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!
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setSeed: aNumber
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super setSeed: aNumber.
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self initializeValues
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!
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values
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^ values
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values:something
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values := something.
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! !
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!RandomLaggedFibonacci methodsFor:'initialization'!
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initialize
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super initialize.
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self drift: 1.
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self setSeed: (OperatingSystem getMicrosecondTime).
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self initializeValueStorage.
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self initializeValues
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!
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initializeValueStorage
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|newValues|
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newValues := Array new:self largeLag.
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self values:newValues
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!
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initializeValues
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|random|
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random := RandomParkMiller new.
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random seed:self seed.
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1 to:self values size do:[:eachIndex |
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self values at:eachIndex put:random next
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]
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! !
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!RandomLaggedFibonacci methodsFor:'private'!
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increaseDrift
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|newDrift|
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newDrift := self drift = self largeLag
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ifTrue:[1]
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ifFalse:[self drift + 1].
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self drift:newDrift
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!
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indexForLag: aLag
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| answer |
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answer := self drift - aLag.
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^ answer > 0
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ifTrue: [answer]
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ifFalse: [answer + self largeLag]
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!
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largeLag
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^ 258
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!
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largeLagValue
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^ self values at: self drift
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!
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smallLag
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^ 83
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!
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smallLagValue
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| index |
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index := self indexForLag: self smallLag.
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^ self values at: index
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! !
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!RandomLaggedFibonacci class methodsFor:'documentation'!
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version_CVS
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^ '$Header: /cvs/stx/stx/libbasic2/RandomLaggedFibonacci.st,v 1.1 2009-10-04 20:05:58 cg Exp $'
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! !
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