prism-accumulation/prism/src/explicit/MDPGeneric.java

//==============================================================================
//	
//	Copyright (c) 2002-
//	Authors:
//	* Dave Parker <david.parker@comlab.ox.ac.uk> (University of Oxford)
//	
//------------------------------------------------------------------------------
//	
//	This file is part of PRISM.
//	
//	PRISM is free software; you can redistribute it and/or modify
//	it under the terms of the GNU General Public License as published by
//	the Free Software Foundation; either version 2 of the License, or
//	(at your option) any later version.
//	
//	PRISM is distributed in the hope that it will be useful,
//	but WITHOUT ANY WARRANTY; without even the implied warranty of
//	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//	GNU General Public License for more details.
//	
//	You should have received a copy of the GNU General Public License
//	along with PRISM; if not, write to the Free Software Foundation,
//	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//	
//==============================================================================

package explicit;

import java.util.BitSet;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.PrimitiveIterator.OfInt;

import common.IterableStateSet;

/**
 * Interface for classes that provide (read) access to an explicit-state MDP,
 * gathering the generic methods, i.e., those that are independent of the
 * underlying value type used for the transition probabilities.
 * <br>
 * This allows use of these methods e.g. in the explicit and parametric engines.
 */
public interface MDPGeneric<Value> extends NondetModel
{
	/**
	 * Get an iterator over the transitions from choice {@code i} of state {@code s}.
	 */
	public Iterator<Entry<Integer, Value>> getTransitionsIterator(int s, int i);

	/**
	 * Perform a single step of precomputation algorithm Prob0, i.e., for states i in {@code subset},
	 * set bit i of {@code result} iff, for all/some choices,
	 * there is a transition to a state in {@code u}.
	 * Quantification over choices is determined by {@code forall}.
	 * @param subset Only compute for these states
	 * @param u Set of states {@code u}
	 * @param forall For-all or there-exists (true=for-all, false=there-exists)
	 * @param result Store results here
	 */
	public default void prob0step(final BitSet subset, final BitSet u, final boolean forall, final BitSet result)
	{
		for (OfInt it = new IterableStateSet(subset, getNumStates()).iterator(); it.hasNext();) {
			final int s = it.nextInt();
			boolean b1 = forall; // there exists or for all
			for (int choice = 0, numChoices = getNumChoices(s); choice < numChoices; choice++) {
				boolean b2 = someSuccessorsInSet(s, choice, u);
				if (forall) {
					if (!b2) {
						b1 = false;
						break;
					}
				} else {
					if (b2) {
						b1 = true;
						break;
					}
				}
			}
			result.set(s, b1);
		}
	}

	/**
	 * Perform a single step of precomputation algorithm Prob1A, i.e., for states i in {@code subset},
	 * set bit i of {@code result} iff, for all choices,
	 * there is a transition to a state in {@code v} and all transitions go to states in {@code u}.
	 * @param subset Only compute for these states
	 * @param u Set of states {@code u}
	 * @param v Set of states {@code v}
	 * @param result Store results here
	 */
	public default void prob1Astep(BitSet subset, BitSet u, BitSet v, BitSet result)
	{
		boolean b1;
		for (OfInt it = new IterableStateSet(subset, getNumStates()).iterator(); it.hasNext();) {
			final int s = it.nextInt();
			b1 = true;
			for (int choice = 0, numChoices = getNumChoices(s); choice < numChoices; choice++) {
				if (!(successorsSafeAndCanReach(s, choice, u, v))) {
					b1 = false;
					break;
				}
			}
			result.set(s, b1);
		}
	}

	/**
	 * Perform a single step of precomputation algorithm Prob1E, i.e., for states i in {@code subset},
	 * set bit i of {@code result} iff, for some choice,
	 * there is a transition to a state in {@code v} and all transitions go to states in {@code u}.
	 * Optionally, store optimal (memoryless) strategy info for 1 states.
	 * @param subset Only compute for these states
	 * @param u Set of states {@code u}
	 * @param v Set of states {@code v}
	 * @param result Store results here
	 * @param strat Storage for (memoryless) strategy choice indices (ignored if null)
	 */
	public default void prob1Estep(BitSet subset, BitSet u, BitSet v, BitSet result, int strat[])
	{
		int stratCh = -1;
		boolean b1;
		for (OfInt it = new IterableStateSet(subset, getNumStates()).iterator(); it.hasNext();) {
			final int s = it.nextInt();
			b1 = false;
			for (int choice = 0, numChoices = getNumChoices(s); choice < numChoices; choice++) {
				if (successorsSafeAndCanReach(s, choice, u, v)) {
					b1 = true;
					// If strategy generation is enabled, remember optimal choice
					if (strat != null)
						stratCh = choice;
					break;
				}
			}
			// If strategy generation is enabled, store optimal choice
			// (only if this the first time we add the state to S^yes)
			if (strat != null & b1 & !result.get(s)) {
				strat[s] = stratCh;
			}
			// Store result
			result.set(s, b1);
		}
	}

	/**
	 * Perform a single step of precomputation algorithm Prob1, i.e., for states i in {@code subset},
	 * set bit i of {@code result} iff, for all/some choices,
	 * there is a transition to a state in {@code v} and all transitions go to states in {@code u}.
	 * Quantification over choices is determined by {@code forall}.
	 * @param subset Only compute for these states
	 * @param u Set of states {@code u}
	 * @param v Set of states {@code v}
	 * @param forall For-all or there-exists (true=for-all, false=there-exists)
	 * @param result Store results here
	 */
	public default void prob1step(BitSet subset, BitSet u, BitSet v, boolean forall, BitSet result)
	{
		boolean b1, b2;
		for (OfInt it = new IterableStateSet(subset, getNumStates()).iterator(); it.hasNext();) {
			final int s = it.nextInt();
			b1 = forall; // there exists or for all
			for (int choice = 0, numChoices = getNumChoices(s); choice < numChoices; choice++) {
				b2 = successorsSafeAndCanReach(s, choice, u, v);
				if (forall) {
					if (!b2) {
						b1 = false;
						break;
					}
				} else {
					if (b2) {
						b1 = true;
						break;
					}
				}
			}
			result.set(s, b1);
		}
	}

	/**
	 * Perform a single step of precomputation algorithm Prob1 for a single state/choice,
	 * i.e., return whether there is a transition to a state in {@code v} and all transitions go to states in {@code u}.
	 * @param s State (row) index
	 * @param i Choice index
	 * @param u Set of states {@code u}
	 * @param v Set of states {@code v}
	 */
	public default boolean prob1stepSingle(int s, int i, BitSet u, BitSet v)
	{
		return successorsSafeAndCanReach(s, i, u, v);
	}

}