--- /dev/null
+/*
+ * Copyright (c) 2003-2005 The BISON Project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+package peersim.util;
+
+/**
+* A class that can keep track of some statistics like variance, average, min,
+* max incrementally. That is, when adding a new data item, it updates the
+* statistics.
+*/
+public class IncrementalStats {
+
+
+// ===================== fields ========================================
+// =====================================================================
+
+
+private double min;
+
+private double max;
+
+private double sum;
+
+private double sqrsum;
+
+private int n;
+
+private int countmin;
+
+private int countmax;
+
+// ====================== initialization ==============================
+// ====================================================================
+
+
+/** Calls {@link #reset}. */
+public IncrementalStats() { reset(); }
+
+// --------------------------------------------------------------------
+
+/** Resets the statistics to reflect the zero elements set.
+* Min and max are set to positive and negative infinity, respectively.
+*/
+public void reset() {
+
+ countmin=0;
+ countmax=0;
+ min = Double.POSITIVE_INFINITY;
+ max = Double.NEGATIVE_INFINITY;
+ sum = 0.0;
+ sqrsum = 0.0;
+ n = 0;
+}
+
+
+// ======================== methods ===================================
+// ====================================================================
+
+
+/** Updates the statistics according to this element. It calls
+* <code>add(item,1)</code>.
+* @see #add(double,int) */
+public final void add( double item ) { add(item,1); }
+
+// --------------------------------------------------------------------
+
+/** Updates the statistics assuming element <code>item</code> is added
+* <code>k</code> times.*/
+public void add( double item, int k ) {
+
+ if( item < min )
+ {
+ min = item;
+ countmin = 0;
+ }
+ if( item == min ) countmin+=k;
+ if( item > max )
+ {
+ max = item;
+ countmax = 0;
+ }
+ if(item == max) countmax+=k;
+ n+=k;
+ if( k == 1 )
+ {
+ sum += item;
+ sqrsum += item*item;
+ }
+ else
+ {
+ sum += item*k;
+ sqrsum += item*item*k;
+ }
+}
+
+// --------------------------------------------------------------------
+
+/** The number of data items processed so far */
+public int getN() { return n; }
+
+// --------------------------------------------------------------------
+
+/** The maximum of the data items */
+public double getMax() { return max; }
+
+// --------------------------------------------------------------------
+
+/** The minimum of the data items */
+public double getMin() { return min; }
+
+// --------------------------------------------------------------------
+
+/** Returns the number of data items whose value equals the maximum. */
+public int getMaxCount() { return countmax; }
+
+// --------------------------------------------------------------------
+
+/** Returns the number of data items whose value equals the minimum. */
+public int getMinCount() { return countmin; }
+
+// --------------------------------------------------------------------
+
+/** The sum of the data items */
+public double getSum() { return sum; }
+
+// --------------------------------------------------------------------
+
+/** The sum of the squares of the data items */
+public double getSqrSum() { return sqrsum; }
+
+// --------------------------------------------------------------------
+
+/** The average of the data items */
+public double getAverage() { return sum/n; }
+
+// --------------------------------------------------------------------
+
+/** The empirical variance of the data items. Guaranteed to be larger or
+equal to 0.0. If due to rounding errors the value becomes negative,
+it returns 0.0.*/
+public double getVar() {
+
+ double var=
+ (((double)n) / (n-1)) * (sqrsum/n - getAverage()*getAverage());
+ return (var>=0.0?var:0.0);
+ // XXX note that we have very little possibility to increase numeric
+ // stability if this class is "greedy", ie, if it has no memory
+ // In a more precise implementation we could delay the calculation of
+ // statistics and store the data in some intelligent structure
+}
+
+// --------------------------------------------------------------------
+
+/** the empirical standard deviation of the data items */
+public double getStD() { return Math.sqrt(getVar()); }
+
+// --------------------------------------------------------------------
+
+/**
+* Prints the following quantities separated by spaces in a single line
+* in this order.
+* Minimum, maximum, number of items, average, variance, number of minimal
+* items, number of maximal items.
+*/
+public String toString() {
+
+ return min+" "+max+" "+n+" "+sum/n+" "+getVar()+" "+
+ countmin+" "+countmax;
+}
+
+}
+
