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Declarative Machine Learning
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.sysml.lops.compile;
import java.util.Comparator;
import org.apache.sysml.lops.Lop;
/**
*
* Comparator class used in sorting the LopDAG in topological order. Refer to
* doTopologicalSort_strict_order() in dml/lops/compile/Dag.java
*
* Topological sort guarantees the following:
*
* 1) All lops with level i appear before any lop with level greater than i
* (source nodes are at level 0)
*
* 2) Within a given level, nodes are ordered by their ID i.e., by the other in
* which they are created
*
* compare() method is designed to respect the above two requirements.
*
* @param class extending Lop
*/
public class LopComparator
implements Comparator
{
@Override
public int compare(N o1, N o2) {
if (o1.getLevel() < o2.getLevel())
return -1; // o1 is less than o2
else if (o1.getLevel() > o2.getLevel())
return 1; // o1 is greater than o2
else {
if (o1.getID() < o2.getID())
return -1; // o1 is less than o2
else if (o1.getID() > o2.getID())
return 1; // o1 is greater than o2
else
throw new RuntimeException("Unexpected error: ID's of two lops are same.");
}
}
}