/**
  * Creates a partial mapping.
  *
  * <p>Initially, no element is mapped to any other:
  *
  * <table border="1">
  * <caption>Example</caption>
  * <tr>
  * <th>source</th>
  * <td>0</td>
  * <td>1</td>
  * <td>2</td>
  * </tr>
  * <tr>
  * <th>target</th>
  * <td>-1</td>
  * <td>-1</td>
  * <td>-1</td>
  * </tr>
  * </table>
  *
  * <table border="1">
  * <caption>Example</caption>
  * <tr>
  * <th>target</th>
  * <td>0</td>
  * <td>1</td>
  * <td>2</td>
  * <td>3</td>
  * </tr>
  * <tr>
  * <th>source</th>
  * <td>-1</td>
  * <td>-1</td>
  * <td>-1</td>
  * <td>-1</td>
  * </tr>
  * </table>
  *
  * @param sourceCount Number of source elements
  * @param targetCount Number of target elements
  * @param mappingType Mapping type; must not allow multiple sources per target or multiple
  *     targets per source
  */
 public PartialMapping(int sourceCount, int targetCount, MappingType mappingType) {
   this.mappingType = mappingType;
   assert mappingType.isSingleSource() : mappingType;
   assert mappingType.isSingleTarget() : mappingType;
   this.sources = new int[targetCount];
   this.targets = new int[sourceCount];
   Arrays.fill(sources, -1);
   Arrays.fill(targets, -1);
 }
 /**
  * Creates a partial mapping from a list. For example, <code>
  * PartialMapping({1, 2, 4}, 6)</code> creates the mapping
  *
  * <table border="1">
  * <caption>Example</caption>
  * <tr>
  * <th>source</th>
  * <td>0</td>
  * <td>1</td>
  * <td>2</td>
  * <td>3</td>
  * <td>4</td>
  * <td>5</td>
  * </tr>
  * <tr>
  * <th>target</th>
  * <td>-1</td>
  * <td>0</td>
  * <td>1</td>
  * <td>-1</td>
  * <td>2</td>
  * <td>-1</td>
  * </tr>
  * </table>
  *
  * @param sourceList List whose i'th element is the source of target #i
  * @param sourceCount Number of elements in the source domain
  * @param mappingType Mapping type, must be {@link
  *     org.eigenbase.util.mapping.MappingType#PARTIAL_SURJECTION} or stronger.
  */
 public PartialMapping(List<Integer> sourceList, int sourceCount, MappingType mappingType) {
   this.mappingType = mappingType;
   assert mappingType.isSingleSource();
   assert mappingType.isSingleTarget();
   int targetCount = sourceList.size();
   this.targets = new int[sourceCount];
   this.sources = new int[targetCount];
   Arrays.fill(sources, -1);
   for (int i = 0; i < sourceList.size(); ++i) {
     final int source = sourceList.get(i);
     sources[i] = source;
     if (source >= 0) {
       targets[source] = i;
     } else {
       assert !this.mappingType.isMandatorySource();
     }
   }
 }