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wip on Markov chain

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Zlatin Balevsky 2020-10-20 16:19:36 +01:00
parent 315f29c668
commit 8798e83ab7
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1 changed files with 48 additions and 47 deletions
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95
core/src/main/groovy/com/muwire/core/hostcache/HostMCProfile.groovy
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@ -2,7 +2,7 @@ package com.muwire.core.hostcache
import java.math.RoundingMode
import static com.muwire.core.connection.ConnectionAttemptStatus.*
import com.muwire.core.connection.ConnectionAttemptStatus
import groovy.sql.GroovyRowResult
@ -19,6 +19,9 @@ class HostMCProfile {
private final BigDecimal RS, RR, RF
private final BigDecimal FS, FR, FF
// start with S
ConnectionAttemptStatus state = ConnectionAttemptStatus.SUCCESSFUL
/**
* constructs an "optimistic" predictor for newly discovered hosts.
*/
@ -62,52 +65,50 @@ class HostMCProfile {
FF.setScale(SCALE, MODE)
}
/**
* @param current status of this host
* @param nextStatus the next status of this host
* @return probability of such status
*/
private BigDecimal transition(def currentStatus, def nextStatus) {
switch(currentStatus) {
case SUCCESSFUL :
switch(nextStatus) {
case SUCCESSFUL : return SS
case REJECTED : return SR
case FAILED : return SF
}
case REJECTED :
switch(nextStatus) {
case SUCCESSFUL : return RS
case REJECTED : return RR
case FAILED : return RF
}
case FAILED :
switch(nextStatus) {
case SUCCESSFUL : return FS
case REJECTED : return FR
case FAILED : return FF
}
}
}
/**
* @param lastStatus last observed status
* @param periods how many periods ago
* @return probability of next status being SUCCESSFUL
*/
public BigDecimal connectSuccessProbability(def lastStatus, int periods) {
if (periods == 0) {
return transition(lastStatus, SUCCESSFUL)
} else {
def toSuccess = transition(lastStatus, SUCCESSFUL)
def toReject = transition(lastStatus, REJECTED)
def toFail = transition(lastStatus, FAILED)
final newPeriods = periods - 1
BigDecimal rv = toSuccess * connectSuccessProbability(SUCCESSFUL, newPeriods) +
toReject * connectSuccessProbability(REJECTED, newPeriods) +
toFail * connectSuccessProbability(FAILED, newPeriods)
rv.setScale(SCALE, MODE)
return rv
ConnectionAttemptStatus transition() {
SortedMap<BigDecimal, ConnectionAttemptStatus> ignitionMap = new TreeMap<>()
switch(state) {
case ConnectionAttemptStatus.SUCCESSFUL :
ignitionMap.put(SS, ConnectionAttemptStatus.SUCCESSFUL)
ignitionMap.put(SR, ConnectionAttemptStatus.REJECTED)
ignitionMap.put(SF, ConnectionAttemptStatus.FAILED)
break
case ConnectionAttemptStatus.REJECTED :
ignitionMap.put(RS, ConnectionAttemptStatus.SUCCESSFUL)
ignitionMap.put(RR, ConnectionAttemptStatus.REJECTED)
ignitionMap.put(RF, ConnectionAttemptStatus.FAILED)
break
case ConnectionAttemptStatus.FAILED:
ignitionMap.put(FS, ConnectionAttemptStatus.SUCCESSFUL)
ignitionMap.put(FR, ConnectionAttemptStatus.REJECTED)
ignitionMap.put(FF, ConnectionAttemptStatus.FAILED)
break
}
BigDecimal[] probs = new BigDecimal[3]
ConnectionAttemptStatus[] states = new ConnectionAttemptStatus[3]
Iterator<BigDecimal> iter = ignitionMap.keySet().iterator()
probs[0] = iter.next()
states[0] = ignitionMap.get(probs[0])
probs[1] = iter.next()
states[1] = ignitionMap.get(probs[1])
probs[2] = iter.next()
states[2] = ignitionMap.get(probs[2])
probs[1] += probs[0]
probs[2] += probs[1]
final double random = Math.random()
if (random < probs[0])
state = states[0]
else if (random < probs[1])
state = states[1]
else
state = states[2]
state
}
}