analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/internal/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java

   1 /*******************************************************************************
   2  * Copyright (c) 2015, 2016 Ericsson
   3  *
   4  * All rights reserved. This program and the accompanying materials are made
   5  * available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors:
  10  *     Bernd Hufmann - Initial API and implementation
  11  *******************************************************************************/
  12 package org.eclipse.tracecompass.internal.analysis.timing.core.segmentstore.statistics;
  13
  14 import org.eclipse.tracecompass.segmentstore.core.ISegment;
  15
  16 /**
  17  * Class to calculate simple segment store statistics (min, max, average)
  18  *
  19  * @author Bernd Hufmann
  20  */
  21 public class SegmentStoreStatistics {
  22     private long fMin;
  23     private long fMax;
  24     private long fNbSegments;
  25     private double fAverage;
  26     private double fVariance;
  27
  28     /**
  29      * Constructor
  30      */
  31     public SegmentStoreStatistics() {
  32         fMin = Long.MAX_VALUE;
  33         fMax = Long.MIN_VALUE;
  34         fNbSegments = 0;
  35         fAverage = 0.0;
  36         fVariance = 0.0;
  37     }
  38
  39     /**
  40      * Get minimum value
  41      *
  42      * @return minimum value
  43      */
  44     public long getMin() {
  45         return fMin;
  46     }
  47
  48     /**
  49      * Get maximum value
  50      *
  51      * @return maximum value
  52      */
  53     public long getMax() {
  54         return fMax;
  55     }
  56
  57     /**
  58      * Get number of segments analyzed
  59      *
  60      * @return number of segments analyzed
  61      */
  62     public long getNbSegments() {
  63         return fNbSegments;
  64     }
  65
  66     /**
  67      * Gets the arithmetic average
  68      *
  69      * @return arithmetic average
  70      */
  71     public double getAverage() {
  72         return fAverage;
  73     }
  74
  75     /**
  76      * Gets the standard deviation of the segments, uses the online algorithm
  77      * shown here <a href=
  78      * "https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm">
  79      * Wikipedia article of dec 3 2015 </a>
  80      *
  81      * @return the standard deviation of the segment store, will return NaN if
  82      *         there are less than 3 elements
  83      */
  84     public double getStdDev() {
  85         return fNbSegments > 2 ? Math.sqrt(fVariance / (fNbSegments - 1)) : Double.NaN;
  86     }
  87
  88     /**
  89      * Update the statistics based on a given segment
  90      * <p>
  91      * This is an online algorithm and must retain a complexity of O(1)
  92      *
  93      * @param segment
  94      *            the segment used for the update
  95      */
  96     public void update(ISegment segment) {
  97         long value = segment.getLength();
  98         /*
  99          * Min and max are trivial, as well as number of segments
 100          */
 101         fMin = Math.min(fMin, value);
 102         fMax = Math.max(fMax, value);
 103
 104         fNbSegments++;
 105         /*
 106          * The running mean is not trivial, see proof in javadoc.
 107          */
 108         double delta = value - fAverage;
 109         fAverage += delta / fNbSegments;
 110         fVariance += delta * (value - fAverage);
 111     }
 112 }