/*
* 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.jena.sparql.expr.aggregate.lib;
import org.apache.jena.sparql.expr.ExprEvalException ;
public class AccStatLib {
/** Calculate the variance (sample) */
public static double calcVarianceSample(double sumSquared, double sum, long count) {
// (N*sum(?x*?x) - sum(?x) ) / N*(N-1)
return calcVariance$(sumSquared, sum, count, count-1) ;
}
/** Calculate the variance (population) */
public static double calcVariancePopulation(double sumSquared, double sum, long N) {
return calcVariance$(sumSquared, sum, N, N) ;
}
// Engine.
static private double calcVariance$(double sumSquared, double sum, long N, long N1) {
// System.out.printf("sum = %f, sumSq = %f, N=%d\n", sum, sumSquared, N) ;
if ( N <= 0 )
throw new ExprEvalException("N= "+N) ;
if ( N1 == 0 )
throw new ExprEvalException("Sample size one") ;
double x = sumSquared - (sum*sum)/N ;
x = x / N1 ;
return x ;
}
}