/*
* 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.commons.math.random;
import java.util.Collection;
/**
* Random data generation utilities.
* @version $Id: RandomData.java 1131229 2011-06-03 20:49:25Z luc $
*/
public interface RandomData {
/**
* Generates a random string of hex characters of length
* <code>len</code>.
* <p>
* The generated string will be random, but not cryptographically
* secure. To generate cryptographically secure strings, use
* <code>nextSecureHexString</code></p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>len > 0</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param len the length of the string to be generated
* @return random string of hex characters of length <code>len</code>
*/
String nextHexString(int len);
/**
* Generates a uniformly distributed random integer between
* <code>lower</code> and <code>upper</code> (endpoints included).
* <p>
* The generated integer will be random, but not cryptographically secure.
* To generate cryptographically secure integer sequences, use
* <code>nextSecureInt</code>.</p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>lower < upper</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param lower lower bound for generated integer
* @param upper upper bound for generated integer
* @return a random integer greater than or equal to <code>lower</code>
* and less than or equal to <code>upper</code>.
*/
int nextInt(int lower, int upper);
/**
* Generates a uniformly distributed random long integer between
* <code>lower</code> and <code>upper</code> (endpoints included).
* <p>
* The generated long integer values will be random, but not
* cryptographically secure.
* To generate cryptographically secure sequences of longs, use
* <code>nextSecureLong</code></p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>lower < upper</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param lower lower bound for generated integer
* @param upper upper bound for generated integer
* @return a random integer greater than or equal to <code>lower</code>
* and less than or equal to <code>upper</code>.
*/
long nextLong(long lower, long upper);
/**
* Generates a random string of hex characters from a secure random
* sequence.
* <p>
* If cryptographic security is not required,
* use <code>nextHexString()</code>.</p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>len > 0</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
* @param len length of return string
* @return the random hex string
*/
String nextSecureHexString(int len);
/**
* Generates a uniformly distributed random integer between
* <code>lower</code> and <code>upper</code> (endpoints included)
* from a secure random sequence.
* <p>
* Sequences of integers generated using this method will be
* cryptographically secure. If cryptographic security is not required,
* <code>nextInt</code> should be used instead of this method.</p>
* <p>
* <strong>Definition</strong>:
* <a href="http://en.wikipedia.org/wiki/Cryptographically_secure_pseudo-random_number_generator">
* Secure Random Sequence</a></p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>lower < upper</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param lower lower bound for generated integer
* @param upper upper bound for generated integer
* @return a random integer greater than or equal to <code>lower</code>
* and less than or equal to <code>upper</code>.
*/
int nextSecureInt(int lower, int upper);
/**
* Generates a random long integer between <code>lower</code>
* and <code>upper</code> (endpoints included).
* <p>
* Sequences of long values generated using this method will be
* cryptographically secure. If cryptographic security is not required,
* <code>nextLong</code> should be used instead of this method.</p>
* <p>
* <strong>Definition</strong>:
* <a href="http://en.wikipedia.org/wiki/Cryptographically_secure_pseudo-random_number_generator">
* Secure Random Sequence</a></p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>lower < upper</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param lower lower bound for generated integer
* @param upper upper bound for generated integer
* @return a long integer greater than or equal to <code>lower</code>
* and less than or equal to <code>upper</code>.
*/
long nextSecureLong(long lower, long upper);
/**
* Generates a random value from the Poisson distribution with
* the given mean.
* <p>
* <strong>Definition</strong>:
* <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda366j.htm">
* Poisson Distribution</a></p>
* <p>
* <strong>Preconditions</strong>: <ul>
* <li>The specified mean <i>must</i> be positive (otherwise an
* IllegalArgumentException is thrown.)</li>
* </ul></p>
* @param mean Mean of the distribution
* @return poisson deviate with the specified mean
*/
long nextPoisson(double mean);
/**
* Generates a random value from the
* Normal (or Gaussian) distribution with the given mean
* and standard deviation.
* <p>
* <strong>Definition</strong>:
* <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3661.htm">
* Normal Distribution</a></p>
* <p>
* <strong>Preconditions</strong>: <ul>
* <li><code>sigma > 0</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
* @param mu Mean of the distribution
* @param sigma Standard deviation of the distribution
* @return random value from Gaussian distribution with mean = mu,
* standard deviation = sigma
*/
double nextGaussian(double mu, double sigma);
/**
* Generates a random value from the exponential distribution
* with expected value = <code>mean</code>.
* <p>
* <strong>Definition</strong>:
* <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3667.htm">
* Exponential Distribution</a></p>
* <p>
* <strong>Preconditions</strong>: <ul>
* <li><code>mu >= 0</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
* @param mean Mean of the distribution
* @return random value from exponential distribution
*/
double nextExponential(double mean);
/**
* Generates a uniformly distributed random value from the open interval
* (<code>lower</code>,<code>upper</code>) (i.e., endpoints excluded).
* <p>
* <strong>Definition</strong>:
* <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3662.htm">
* Uniform Distribution</a> <code>lower</code> and
* <code>upper - lower</code> are the
* <a href = "http://www.itl.nist.gov/div898/handbook/eda/section3/eda364.htm">
* location and scale parameters</a>, respectively.</p>
* <p>
* <strong>Preconditions</strong>:<ul>
* <li><code>lower < upper</code> (otherwise an IllegalArgumentException
* is thrown.)</li>
* </ul></p>
*
* @param lower lower endpoint of the interval of support
* @param upper upper endpoint of the interval of support
* @return uniformly distributed random value between lower
* and upper (exclusive)
*/
double nextUniform(double lower, double upper);
/**
* Generates an integer array of length <code>k</code> whose entries
* are selected randomly, without repetition, from the integers <code>
* 0 through n-1</code> (inclusive).
* <p>
* Generated arrays represent permutations
* of <code>n</code> taken <code>k</code> at a time.</p>
* <p>
* <strong>Preconditions:</strong><ul>
* <li> <code>k <= n</code></li>
* <li> <code>n > 0</code> </li>
* </ul>
* If the preconditions are not met, an IllegalArgumentException is
* thrown.</p>
*
* @param n domain of the permutation
* @param k size of the permutation
* @return random k-permutation of n
*/
int[] nextPermutation(int n, int k);
/**
* Returns an array of <code>k</code> objects selected randomly
* from the Collection <code>c</code>.
* <p>
* Sampling from <code>c</code>
* is without replacement; but if <code>c</code> contains identical
* objects, the sample may include repeats. If all elements of <code>
* c</code> are distinct, the resulting object array represents a
* <a href="http://rkb.home.cern.ch/rkb/AN16pp/node250.html#SECTION0002500000000000000000">
* Simple Random Sample</a> of size
* <code>k</code> from the elements of <code>c</code>.</p>
* <p>
* <strong>Preconditions:</strong><ul>
* <li> k must be less than or equal to the size of c </li>
* <li> c must not be empty </li>
* </ul>
* If the preconditions are not met, an IllegalArgumentException is
* thrown.</p>
*
* @param c collection to be sampled
* @param k size of the sample
* @return random sample of k elements from c
*/
Object[] nextSample(Collection<?> c, int k);
}