org.beedraz.semantics_II.expression.number.real.double64.stat.DoubleSampleVarianceBeed.java Source code

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Here is the source code for org.beedraz.semantics_II.expression.number.real.double64.stat.DoubleSampleVarianceBeed.java

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/*<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.Variance;
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 sample variance of a given set of beeds of type
 * {@link org.beedraz.semantics_II.expression.number.real.RealBeed}.
 *
 * sample_variance(x_1, ..., x_n) = sum((x_i - mean)^2) / (n - 1)
 *
 * @invar getSource() != null ==>
 *        (forAll DoubleBeed db; getSource().get().contains(db); db.getDouble() != null)
 *            ==> getDouble() == sample_variance { db.getDouble() | getSource().get().contains(db)};
 *        If the values of all beeds in the given set are effective,
 *        then the value of the sample variance beed is the sample variance of the values of
 *        all beeds in the given set.
 *        The sample variance of an empty set is {@link Double#NaN}.
 *        The sample variance of a set containing only one element is 0.
 *        e.g. when  getSource() = {1, 2, 3, 4}
 *             then  getDouble() = dividend/divisor
 *             where divisor = 3
 *             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 DoubleSampleVarianceBeed extends AbstractDoubleCommonsMathSetComputationBeed {

    /**
     * @post  getSource() == null;
     * @post  getDouble() == null;
     */
    public DoubleSampleVarianceBeed() {
        this(null);
    }

    /**
     * @post  getSource() == null;
     * @post  getDouble() == null;
     * @post  owner != null ? owner.registerAggregateElement(this);
     */
    public DoubleSampleVarianceBeed(AggregateBeed owner) {
        super(new Variance(true), owner);
    }

    @Override
    public final String getOperatorString() {
        return "sample_variance";
    }

}