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Core sketch algorithms used alone and by other Java repositories in the DataSketches library.
/*
* 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.datasketches.common;
import static org.apache.datasketches.common.BoundsOnBinomialProportions.approximateLowerBoundOnP;
import static org.apache.datasketches.common.BoundsOnBinomialProportions.approximateUpperBoundOnP;
/**
* This class is used to compute the bounds on the estimate of the ratio |B| / |A|, where:
*
* - |A| is the unknown size of a set A of unique identifiers.
* - |B| is the unknown size of a subset B of A.
* - a = |SA| is the observed size of a sample of A
* that was obtained by Bernoulli sampling with a known inclusion probability f.
* - b = |SA ∩ B| is the observed size of a subset
* of SA.
*
*
* @author Kevin Lang
*/
public final class BoundsOnRatiosInSampledSets {
private static final double NUM_STD_DEVS = 2.0; //made a constant to simplify interface.
private BoundsOnRatiosInSampledSets() {}
/**
* Return the approximate lower bound based on a 95% confidence interval
* @param a See class javadoc
* @param b See class javadoc
* @param f the inclusion probability used to produce the set with size a and should
* generally be less than 0.5. Above this value, the results not be reliable.
* When f = 1.0 this returns the estimate.
* @return the approximate upper bound
*/
public static double getLowerBoundForBoverA(final long a, final long b, final double f) {
checkInputs(a, b, f);
if (a == 0) { return 0.0; }
if (f == 1.0) { return (double) b / a; }
return approximateLowerBoundOnP(a, b, NUM_STD_DEVS * hackyAdjuster(f));
}
/**
* Return the approximate upper bound based on a 95% confidence interval
* @param a See class javadoc
* @param b See class javadoc
* @param f the inclusion probability used to produce the set with size a.
* @return the approximate lower bound
*/
public static double getUpperBoundForBoverA(final long a, final long b, final double f) {
checkInputs(a, b, f);
if (a == 0) { return 1.0; }
if (f == 1.0) { return (double) b / a; }
return approximateUpperBoundOnP(a, b, NUM_STD_DEVS * hackyAdjuster(f));
}
/**
* Return the estimate of b over a
* @param a See class javadoc
* @param b See class javadoc
* @return the estimate of b over a
*/
public static double getEstimateOfBoverA(final long a, final long b) {
checkInputs(a, b, 0.3);
if (a == 0) { return 0.5; }
return (double) b / a;
}
/**
* Return the estimate of A. See class javadoc.
* @param a See class javadoc
* @param f the inclusion probability used to produce the set with size a.
* @return the approximate lower bound
*/
public static double getEstimateOfA(final long a, final double f) {
checkInputs(a, 1, f);
return a / f;
}
/**
* Return the estimate of B. See class javadoc.
* @param b See class javadoc
* @param f the inclusion probability used to produce the set with size b.
* @return the approximate lower bound
*/
public static double getEstimateOfB(final long b, final double f) {
checkInputs(b + 1, b, f);
return b / f;
}
/**
* This hackyAdjuster is tightly coupled with the width of the confidence interval normally
* specified with number of standard deviations. To simplify this interface the number of
* standard deviations has been fixed to 2.0, which corresponds to a confidence interval of
* 95%.
* @param f the inclusion probability used to produce the set with size a.
* @return the hacky Adjuster
*/
private static double hackyAdjuster(final double f) {
final double tmp = Math.sqrt(1.0 - f);
return (f <= 0.5) ? tmp : tmp + (0.01 * (f - 0.5));
}
static void checkInputs(final long a, final long b, final double f) {
if ( ( (a - b) | (a) | (b) ) < 0) { //if any group goes negative
throw new SketchesArgumentException(
"a must be >= b and neither a nor b can be < 0: a = " + a + ", b = " + b);
}
if ((f > 1.0) || (f <= 0.0)) {
throw new SketchesArgumentException("Required: ((f <= 1.0) && (f > 0.0)): " + f);
}
}
}
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