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100 lines
3.6 KiB
100 lines
3.6 KiB
//==============================================================================
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//
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// Copyright (c) 2002-
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// Authors:
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// * Dave Parker <david.parker@comlab.ox.ac.uk> (University of Oxford)
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//
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//------------------------------------------------------------------------------
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//
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// This file is part of PRISM.
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//
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// PRISM is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// (at your option) any later version.
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//
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// PRISM is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with PRISM; if not, write to the Free Software Foundation,
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// Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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//
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//==============================================================================
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package simulator.sampler;
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import simulator.*;
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import prism.*;
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import parser.ast.*;
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public class SamplerRewardCumulCont extends SamplerDouble
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{
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private double timeBound;
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private int rewardStructIndex;
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/**
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* Construct a sampler for a (continuous-time) cumulative reward property.
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* Passed in ExpressionTemporal should be a property of this type.
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* Reward structure index should also be specified.
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* All constants should have already been evaluated/replaced.
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*/
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public SamplerRewardCumulCont(ExpressionTemporal expr, int rewardStructIndex) throws PrismException
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{
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// Make sure expression is of the correct type
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// Then extract other required info
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if (expr.getOperator() != ExpressionTemporal.R_C)
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throw new PrismException("Error creating Sampler");
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timeBound = expr.getUpperBound().evaluateDouble();
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this.rewardStructIndex = rewardStructIndex;
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// Initialise sampler info
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reset();
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resetStats();
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}
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@Override
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public boolean update(Path path, TransitionList transList) throws PrismLangException
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{
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// If the answer is already known we should do nothing
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if (valueKnown)
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return true;
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// As soon as time bound exceeded, compute reward total
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if (path.getTotalTime() >= timeBound) {
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valueKnown = true;
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value = path.getTotalCumulativeReward(rewardStructIndex);
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// Compute excess time, i.e. how long ago time bound was reached
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double excessTime = path.getTotalTime() - timeBound;
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// If this is > 0 (very likely, unless time bound = 0),
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// need to subtract reward accumulated in excess time and transition reward
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// Note that this cannot be the case for the first state of path,
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// so the call to getTimeInPreviousState() is safe.
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if (excessTime > 0) {
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// Note: Time so far > 0 so cannot be first state,
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// so safe to look at previous state.
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value -= path.getPreviousStateReward(rewardStructIndex) * excessTime;
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value -= path.getPreviousTransitionReward(rewardStructIndex);
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}
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}
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// Or, if we are now at a deadlock
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else if (transList != null && transList.isDeadlock()) {
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valueKnown = true;
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value = path.getTotalCumulativeReward(rewardStructIndex);
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// Compute remaining time, i.e. how long left until time bound will be reached
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double remainingTime = timeBound - path.getTotalTime();
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value += path.getCurrentStateReward(rewardStructIndex) * remainingTime;
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}
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return valueKnown;
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}
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@Override
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public boolean needsBoundedNumSteps()
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{
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// Always bounded (although we don't know the exact num steps, just the time bound)
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return true;
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}
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}
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