Java tutorial
/*<license> Copyright 2007 - $Date$ by the authors mentioned below. Licensed 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. </license>*/ package org.beedraz.semantics_II.expression.number.real.double64.stat; import static org.ppwcode.metainfo_I.License.Type.APACHE_V2; import org.apache.commons.math.stat.descriptive.moment.StandardDeviation; import org.beedraz.semantics_II.aggregate.AggregateBeed; import org.ppwcode.metainfo_I.Copyright; import org.ppwcode.metainfo_I.License; import org.ppwcode.metainfo_I.vcs.SvnInfo; /** * A beed that computes the population standard deviation of a given set of beeds of type * {@link org.beedraz.semantics_II.expression.number.real.RealBeed}. * * population_standard_deviation(x_1, ..., x_n) = Math.sqrt(sum((x_i - mean)^2) / n) * * @invar getSource() != null ==> * (forAll DoubleBeed db; getSource().get().contains(db); db.getDouble() != null) * ==> getDouble() == population_standard_deviation { db.getDouble() | getSource().get().contains(db)}; * If the values of all beeds in the given set are effective, then the value * of the population standard deviation beed is the population standard deviation of * the values of all beeds in the given set. * The population standard deviation of an empty set is {@link Double#NaN}. * The population standard deviation of a set containing only one element is 0. * e.g. when getSource() = {1, 2, 3, 4} * then getDouble() = Math.sqrt(dividend/divisor) * where divisor = 4 * and dividend = (1-mean)^2 + (2-mean)^2 + (3-mean)^2 + (4-mean)^2) * and mean = (1 + 2 + 3 + 4)/4 */ @Copyright("2007 - $Date$, Beedraz authors") @License(APACHE_V2) @SvnInfo(revision = "$Revision$", date = "$Date$") public class DoublePopulationStandardDeviationBeed extends AbstractDoubleCommonsMathSetComputationBeed { /** * @post getSource() == null; * @post getDouble() == null; */ public DoublePopulationStandardDeviationBeed() { this(null); } /** * @post getSource() == null; * @post getDouble() == null; * @post owner != null ? owner.registerAggregateElement(this); */ public DoublePopulationStandardDeviationBeed(AggregateBeed owner) { super(new StandardDeviation(false), owner); } @Override public final String getOperatorString() { return "population_standard_deviation"; } }