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InstantiatingEvalContext.java
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/* * Copyright (c) 2006, Regents of the University of California * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * * Neither the name of the University of California, Berkeley nor * the names of its contributors may be used to endorse or promote * products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. */ package blog; import java.util.*; import common.Util;
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Implementation of the EvalContext interface that instantiates new
basic random variables as necessary in response to method calls.
To instantiate a variable, it first instantiates all that variable's
active parents, then samples a value for the variable using its CPD
given those parent values.
When it becomes necessary to instantiate a random variable, a new InstantiatingEvalContext is created to evaluate its dependency model and determine its CPD. We say that the random variable to be instantiated is responsible for the creation of this new InstantiatingEvalContext. For any given InstantiatingEvalContext, there is a sequence of responsible variables that led to its creation. This sequence is passed into the InstantiatingEvalContext constructor (except in the default case where the sequence is empty), in the form of an ordered map from responsible variables to the evaluation contexts that led to those variables. Storing this sequence of responsible variables is useful for debugging, but it also allows us to detect cyclic dependencies. If an InstantiatingEvalContext is about to try determining the CPD for a random variable that's already among its responsible variables, then it raises a fatal error rather than entering an infinite loop. |
public class InstantiatingEvalContext extends ParentRecEvalContext {
| Creates a new InstantiatingEvalContext using the given world. Its sequence of responsible variables is empty. |
public InstantiatingEvalContext(PartialWorld world) {
super(world);
this.respVarsAndContexts = new LinkedHashMap();
}
Creates a new InstantiatingEvalContext with the given sequence
of responsible variables.
which the order of the variables is the
order in which they were reached in the
recursive instantiation process, and each
variable is mapped to the context that
led to it
|
private InstantiatingEvalContext(PartialWorld world,
LinkedHashMap respVarsAndContexts) {
super(world);
this.respVarsAndContexts = respVarsAndContexts;
}
public boolean isInstantiated(BasicVar var) {
return (world.getValue(var) != null);
}
public Object getValue(BasicVar var) {
Object value = world.getValue(var);
if (value == null) {
if (var instanceof VarWithDistrib) {
value = instantiate((VarWithDistrib) var);
} else {
throw new IllegalArgumentException
("Don't know how to instantiate: " + var);
}
}
if (parents.add(var)) {
var.ensureStable();
}
return value;
}
// Note that we don't have to override getSatisfiers, because the
// DefaultEvalContext implementation of getSatisfiers calls getValue
// on the number variable.
| Returns the log of the probability of this InstantiatingEvalContext assigning the values it has assigned to the variables it has instantiated. |
public double getLogProbability() {
return logProb;
}
private Object instantiate(VarWithDistrib var) {
var.ensureStable();
/*
if (Util.verbose()) {
System.out.println("Need to instantiate: " + var);
}
*/
if (respVarsAndContexts.containsKey(var)) {
cycleError(var);
}
// Create a new "child" context and get the distribution for
// var in that context.
respVarsAndContexts.put(var, this);
InstantiatingEvalContext spawn = new InstantiatingEvalContext
(world, respVarsAndContexts);
DependencyModel.Distrib distrib = var.getDistrib(spawn);
logProb += spawn.getLogProbability();
respVarsAndContexts.remove(this);
// Sample new value for var
CondProbDistrib cpd = distrib.getCPD();
List cpdArgs = distrib.getArgValues();
Object newValue = cpd.sampleVal(cpdArgs, var.getType());
logProb += Math.log(cpd.getProb(cpdArgs, newValue));
// Assert any identifiers that are used by var
Object[] args = var.args();
for (int i = 0; i < args.length; ++i) {
if (args[i] instanceof ObjectIdentifier) {
world.assertIdentifier((ObjectIdentifier) args[i]);
}
}
if (newValue instanceof ObjectIdentifier) {
world.assertIdentifier((ObjectIdentifier) newValue);
}
// Actually set value
world.setValue(var, newValue);
/*
if (Util.verbose()) {
System.out.println("Instantiated: " + var);
}
*/
return newValue;
}
private void cycleError(VarWithDistrib var) {
System.err.println("Encountered cycle in context-specific "
+ "dependency graph. Evaluation sequence: ");
for (Iterator iter = respVarsAndContexts.entrySet().iterator();
iter.hasNext(); ) {
Map.Entry entry = (Map.Entry) iter.next();
((EvalContext) entry.getValue()).printEvalTrace(System.err);
System.err.println(entry.getKey());
}
printEvalTrace(System.err);
System.err.println(var);
Util.fatalError("Stopping evaluation to avoid infinite loop.", false);
}
private LinkedHashMap respVarsAndContexts; // VarWithDistrib to EvalContext
private double logProb = 0;
}
This file was generated on Tue Jun 08 17:53:36 PDT 2010 from file InstantiatingEvalContext.java
by the ilog.language.tools.Hilite Java tool written by Hassan Aït-Kaci