OverlappingElvis · August 17, 2017 20:31 · Aug 17, 2017 · Aug 17, 2017 · Aug 10, 2017 · Aug 10, 2017
diff --git a/bathroom.js b/bathroom.js
@@ -101,4 +101,4 @@ var fn = results.falseNegative / samples;
 // Reporting
 console.log('Results after ' + numberOfRuns + ' runs:');
 console.log('Probability of the bathroom being occupied when the sign reads occupied: ' + (tp / (tp + fp)).toPrecision(4));
-console.log('Probability of the bathroom being occupied when the sign reads occupied: ' + (tn / (tn + fn)).toPrecision(4));
+console.log('Probability of the bathroom being vacant when the sign reads vacant: ' + (tn / (tn + fn)).toPrecision(4));
diff --git a/bathroom.js b/bathroom.js
@@ -69,7 +69,7 @@ Person.prototype.useBathroom = function(state) {
 };
 
 // Set number of runs for the model
-var numberOfRuns = 100000;
+var numberOfRuns = 500000;
 // Sample twice per run
 var samples = numberOfRuns * 2;
 
@@ -93,9 +93,12 @@ var results = _(numberOfRuns).chain()
 	.reduce(function(state, person) { return person.useBathroom(state); }, initialState)
 	.value();
 
+var tp = results.truePositive / samples;
+var tn = results.trueNegative / samples;
+var fp = results.falsePositive / samples;
+var fn = results.falseNegative / samples;
+
 // Reporting
 console.log('Results after ' + numberOfRuns + ' runs:');
-console.log('True positive probability: ' + results.truePositive / samples);
-console.log('True negative probability: ' + results.trueNegative / samples);
-console.log('False positive probability: ' + results.falsePositive / samples);
-console.log('False negative probability: ' + results.falseNegative / samples);
+console.log('Probability of the bathroom being occupied when the sign reads occupied: ' + (tp / (tp + fp)).toPrecision(4));
+console.log('Probability of the bathroom being occupied when the sign reads occupied: ' + (tn / (tn + fn)).toPrecision(4));
diff --git a/bathroom.js b/bathroom.js
@@ -97,5 +97,5 @@ var results = _(numberOfRuns).chain()
 console.log('Results after ' + numberOfRuns + ' runs:');
 console.log('True positive probability: ' + results.truePositive / samples);
 console.log('True negative probability: ' + results.trueNegative / samples);
-console.log('True negative probability: ' + results.falsePositive / samples);
+console.log('False positive probability: ' + results.falsePositive / samples);
 console.log('False negative probability: ' + results.falseNegative / samples);
diff --git a/bathroom.js b/bathroom.js
@@ -7,8 +7,12 @@ var VACANT = false;
 
 // Sample a current state
 var knock = function(state) {
-	if (state.sign === state.bathroom) {
-		return _({}).extend(state, { correct: state.correct + 1 });
+	var correct = state.sign === state.bathroom;
+	if (correct && state.sign === OCCUPIED) {
+		return _({}).extend(state, { truePositive: state.truePositive + 1 });
+	}
+	if (correct && state.sign === VACANT) {
+		return _({}).extend(state, { trueNegative: state.trueNegative + 1 });
 	}
 	if (state.sign && !state.bathroom) {
 		return _({}).extend(state, { falsePositive: state.falsePositive + 1 });
@@ -57,7 +61,6 @@ Person.prototype.enterBathroom = function(state) {
 Person.prototype.exitBathroom = function(state) {
 	return this.exitBehavior(state);
 };
-// Use the bathroom and sample each step
 Person.prototype.useBathroom = function(state) {
 	// Enter the bathroom and sample the result
 	var enterState = knock(this.enterBathroom(state));
@@ -66,14 +69,16 @@ Person.prototype.useBathroom = function(state) {
 };
 
 // Set number of runs for the model
-var numberOfRuns = 50000;
+var numberOfRuns = 100000;
 // Sample twice per run
 var samples = numberOfRuns * 2;
-// Initial state
+
+// Initial starting state
 var initialState = {
 	sign: VACANT,
 	bathroom: VACANT,
-	correct: 0,
+	truePositive: 0,
+	trueNegative: 0,
 	falsePositive: 0,
 	falseNegative: 0
 };
@@ -85,13 +90,12 @@ var results = _(numberOfRuns).chain()
 	// Generate as many people as runs
 	.map(function() { return new Person(); })
 	// Work through the runs, returning a final state
-	.reduce(function(state, person) {
-		return person.useBathroom(state);
-	}, initialState)
+	.reduce(function(state, person) { return person.useBathroom(state); }, initialState)
 	.value();
 
 // Reporting
 console.log('Results after ' + numberOfRuns + ' runs:');
-console.log('Correct sign probability: ' + results.correct / samples);
-console.log('False positive probability: ' + results.falsePositive / samples);
+console.log('True positive probability: ' + results.truePositive / samples);
+console.log('True negative probability: ' + results.trueNegative / samples);
+console.log('True negative probability: ' + results.falsePositive / samples);
 console.log('False negative probability: ' + results.falseNegative / samples);
diff --git a/bathroom.js b/bathroom.js
@@ -85,8 +85,8 @@ var results = _(numberOfRuns).chain()
 	// Generate as many people as runs
 	.map(function() { return new Person(); })
 	// Work through the runs, returning a final state
-	.reduce(function(memo, person) {
-		return person.useBathroom(memo);
+	.reduce(function(state, person) {
+		return person.useBathroom(state);
 	}, initialState)
 	.value();
 

diff --git a/bathroom.js b/bathroom.js
@@ -69,8 +69,7 @@ Person.prototype.useBathroom = function(state) {
 var numberOfRuns = 50000;
 // Sample twice per run
 var samples = numberOfRuns * 2;
-
-// Initial starting state
+// Initial state
 var initialState = {
 	sign: VACANT,
 	bathroom: VACANT,

diff --git a/bathroom.js b/bathroom.js
@@ -84,9 +84,7 @@ var results = _(numberOfRuns).chain()
 	// Get a list with length numberOfRuns
 	.range()
 	// Generate as many people as runs
-	.map(function() {
-		return new Person();
-	})
+	.map(function() { return new Person(); })
 	// Work through the runs, returning a final state
 	.reduce(function(memo, person) {
 		return person.useBathroom(memo);

diff --git a/bathroom.js b/bathroom.js
@@ -57,6 +57,7 @@ Person.prototype.enterBathroom = function(state) {
 Person.prototype.exitBathroom = function(state) {
 	return this.exitBehavior(state);
 };
+// Use the bathroom and sample each step
 Person.prototype.useBathroom = function(state) {
 	// Enter the bathroom and sample the result
 	var enterState = knock(this.enterBathroom(state));

diff --git a/bathroom.js b/bathroom.js
@@ -94,7 +94,6 @@ var results = _(numberOfRuns).chain()
 
 // Reporting
 console.log('Results after ' + numberOfRuns + ' runs:');
-console.log(results);
 console.log('Correct sign probability: ' + results.correct / samples);
 console.log('False positive probability: ' + results.falsePositive / samples);
 console.log('False negative probability: ' + results.falseNegative / samples);
diff --git a/bathroom.js b/bathroom.js
@@ -0,0 +1,100 @@
+// underscore.js helpers
+var _ = require('underscore');
+
+// State aliases
+var OCCUPIED = true;
+var VACANT = false;
+
+// Sample a current state
+var knock = function(state) {
+	if (state.sign === state.bathroom) {
+		return _({}).extend(state, { correct: state.correct + 1 });
+	}
+	if (state.sign && !state.bathroom) {
+		return _({}).extend(state, { falsePositive: state.falsePositive + 1 });
+	}
+	return _({}).extend(state, { falseNegative: state.falseNegative + 1 });
+};
+
+// Define behaviors as modifying the current state of the bathroom. Can be invoked as entering or exiting.
+
+// Don't change the state of the sign
+var unobservant = function(state, exit) {
+	return _({}).extend(state, {
+		sign: state.sign,
+		bathroom: !exit
+	});
+};
+// Change the sign when entering, but not on leaving
+var forgetful = function(state, exit) {
+	return _({}).extend(state, {
+		sign: OCCUPIED,
+		bathroom: !exit
+	});
+};
+// Make sure that the sign reflects the actual state of the bathroom
+var conscientious = function(state, exit) {
+	return _({}).extend(state, {
+		sign: !exit,
+		bathroom: !exit
+	});
+};
+// Each behavior is as likely to appear
+var chooseBehavior = _(_.sample).partial([unobservant, forgetful, conscientious]);
+
+// Create a person, randomly choosing a behavior
+var Person = function() {
+	var behavior = chooseBehavior();
+	this.enterBehavior = behavior;
+	// Behavior functionality is based on the exit flag, so we can reuse and partially apply that flag to the exit behavior
+	this.exitBehavior = _(behavior).partial(_, true);
+};
+// Enter bathroom
+Person.prototype.enterBathroom = function(state) {
+	return this.enterBehavior(state);
+};
+// Exit bathroom
+Person.prototype.exitBathroom = function(state) {
+	return this.exitBehavior(state);
+};
+Person.prototype.useBathroom = function(state) {
+	// Enter the bathroom and sample the result
+	var enterState = knock(this.enterBathroom(state));
+	// Exit the bathroom and sample the result
+	return knock(this.exitBathroom(enterState));
+};
+
+// Set number of runs for the model
+var numberOfRuns = 50000;
+// Sample twice per run
+var samples = numberOfRuns * 2;
+
+// Initial starting state
+var initialState = {
+	sign: VACANT,
+	bathroom: VACANT,
+	correct: 0,
+	falsePositive: 0,
+	falseNegative: 0
+};
+
+// Get the results
+var results = _(numberOfRuns).chain()
+	// Get a list with length numberOfRuns
+	.range()
+	// Generate as many people as runs
+	.map(function() {
+		return new Person();
+	})
+	// Work through the runs, returning a final state
+	.reduce(function(memo, person) {
+		return person.useBathroom(memo);
+	}, initialState)
+	.value();
+
+// Reporting
+console.log('Results after ' + numberOfRuns + ' runs:');
+console.log(results);
+console.log('Correct sign probability: ' + results.correct / samples);
+console.log('False positive probability: ' + results.falsePositive / samples);
+console.log('False negative probability: ' + results.falseNegative / samples);