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<HTML><HEAD><TITLE>Random Library</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.53"><LINKREL="HOME"TITLE="Documentation Set for Swarm 2.1.1"HREF="set.html"><LINKREL="UP"TITLE="Reference Guide for Swarm 2.1.1"HREF="book930.html"><LINKREL="PREVIOUS"TITLE="General"HREF="swarm.objectbase.generic.module.html"><LINKREL="NEXT"TITLE="ACGgen"HREF="swarm.random.acggen.protocol.html"></HEAD><BODYCLASS="REFERENCE"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLEWIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Documentation Set for Swarm 2.1.1</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="swarm.objectbase.generic.module.html">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="swarm.random.acggen.protocol.html">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="REFERENCE"><ANAME="SWARM.RANDOM.SGML.REFERENCE"></A><DIVCLASS="TITLEPAGE"><H1CLASS="TITLE">V. Random Library</H1><DIVCLASS="PARTINTRO"><ANAME="AEN12878"></A><TABLECLASS="SIDEBAR"BORDER="1"CELLPADDING="5"><TR><TD><DIVCLASS="SIDEBAR"><P><B>Overview</B></P><P>First, a few thoughts on random number generation. It's hard to do right! The root cause, of course, is that computer algorithms themselves are not truly random. (Hence this library contains pseudo-random generators only.) There are many problems in implementing algorithms correctly and efficiently, and in coming up with good tests for generators and distributions. The history of pseudorandom number generation in simulation work is mostly embarrassing. This library attempts to do a decent job of generating random numbers, as well as documenting how things work and what shortcomings there are. If you want to learn more about random number generation, the bibliography in the <AHREF="http://www.swarm.org"TARGET="_top"><ICLASS="CITETITLE">Swarm User Guide</I></A> has useful notes. Knuth is the main reference in this realm, but too old to describe most of the particular generators used here, many of which are drawn from recent literature. </P></DIV></TD></TR></TABLE><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="SWARM.RANDOM.SGML.SECT1.DEPEND">1. Dependencies</A></H1><P>Following are the other header files imported by <random.h>:</P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING">#import <objectbase.h>#import <random/generators.h>#import <random/distributions.h>#import <random/randomdefs.h>#import <random/randomvars.h></PRE></TD></TR></TABLE><P>The <ICLASS="EMPHASIS">objectbase</I> library interface is included to provide the basic object support. <TTCLASS="FILENAME">randomdefs.h</TT> contains some C preprocessor macros and typedefs used in the library.</P><P>This reference guide contains the object definitions for generators and distributions (see the list above) and also encodes the inheritance structure through the "Protocols that this protocol uses" section of each protocol. Just click on a (sub-)protocol name to see what methods it implements. (You may want to review the section on Protocols in the Objective-C book here!) </P><P>In the protocols described, any protocol that ultimately inherits from CREATABLE defines an object that you can use in your program. (This is part of the Swarm defobj machinery.) In other words, while 'InternalState' is a normal protocol (a list of method definitions), the name `ACGgen' refers to both a protocol and a class that implements that protocol. Similarly, 'GammaDist' defines both a protocol and a class that implements that protocol.</P><P>All generators and distributions ultimately inherit from SwarmObject.</P></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="SWARM.RANDOM.SGML.SECT1.COMPAT">2. Compatibility</A></H1><P></P><UL><LI><DIVCLASS="FORMALPARA"><P><B>1.0.2 -> 1.0.3. </B><ICLASS="EMPHASIS">Note:</I> The new random library does not work in the same way as the old one. This means that some applications that used the random library provided with the 1.0.2 release will be <ICLASS="EMPHASIS">broken</I>. However, porting these applications to the new random library will be fairly easy since large efforts were made to adhere to the standard set with the last version and some backwards compatibility hooks were incorporated. </P></DIV></LI><LI><DIVCLASS="FORMALPARA"><P><B>1.0, 1.1, 1.2, 1.3, 1.3.1, 1.4. </B>There were no major compatibility issues in these releases. </P></DIV></LI></UL></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="SWARM.RANDOM.SGML.SECT1.USAGE">3. Usage Guide</A></H1><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN12909">3.1. Overview</A></H2><P>The <ICLASS="EMPHASIS">random</I> library contains two kinds of objects, the <ICLASS="EMPHASIS">generators</I> which implement different pseudo-random-number algorithms, and the <ICLASS="EMPHASIS">distributions</I> which transform the (uniform) output from the generators into the desired simulated statistical distributions. (The Swarm random library does not implement any <ICLASS="EMPHASIS">true</I> random number generators at this time.) </P></DIV><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN12916">3.2. Usage Guide for Beginners, Advanced Usage Guide and Guide to Generators and Distributions</A></H2><P>All these sections have been relocated to the <AHREF="http://www.swarm.org"TARGET="_top"><ICLASS="CITETITLE">Swarm User Guide</I></A></P></DIV></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="SWARM.RANDOM.SGML.SECT1.SUBCLASS">4. Subclassing Reference</A></H1><P>Random library objects do not do anything exotic during the create phase. The competent programmer may subclass these objects in the normal manner. </P></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="SWARM.RANDOM.SGML.SECT1.IMPL">5. Implementation Notes</A></H1><P>This section provides implementation details for the current version of the random library. </P><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN12927">5.1. General Implementation Notes</A></H2><P>This is release 1.4.1 of the Swarm libraries. It contains version0.8 of the random-number library and version 0.81 of the random librarydocumentation. </P><P>Look at the <AHREF="swarm.random.sgml.reference.html">RandomLibrary Reference</A> for the objects defined in thislibrary.</P><DIVCLASS="FORMALPARA"><P><B>`Fat' vs. `Thin' doubles. </B>Note that distributions which use floating point variates fromtheir generators by default draw `fat' doubles (-getDoubleSample)which use two calls to the basic (32-bit) unsigned int sample method(-getUnsignedSample) in order to fill the 53-bit mantissa of a double.If you don't need this much precision, or want to speed up thedistributions, you can make the distributions use `thin' samples(-getThinDoubleSample) instead. See the note at the top of<TTCLASS="FILENAME">random/distributions.h</TT> for how to change thisbehavior. If you do, be sure to remake Swarm(<TTCLASS="USERINPUT"><B>make</B></TT>, <TTCLASS="USERINPUT"><B>make install</B></TT>).</P></DIV></DIV><DIVCLASS="SECT2"><H2CLASS="SECT2"><ANAME="AEN12938">5.2. Implementation notes for Generators</A></H2><DIVCLASS="FORMALPARA"><P><B>Version 0.8: Changes since version 0.75. </B><P></P><OLTYPE="1"><LI><P>The code was rearranged to conform to create-phaseprotocol (CREATING-SETTING-USING) ordering.</P></LI><LI><P>Some for-loop indices were changed to unsignedintegers to eliminate compiler warnings.</P></LI><LI><P>A few objects (C2LCGXgen, C4LCGXgen, SWBgen, TGFSRgen)were given their own -drop methods to drop internally allocated arraysproperly.</P></LI><LI><P>A new -reset method was added to all generators. Thismethod resets the state of the generator to what it was at creation,or at the point when -setStateFromSeed(s) was last used. Counters arealso reset.</P></LI></OL> </P></DIV><DIVCLASS="FORMALPARA"><P><B>Version 0.75: Changes since version 0.7. </B><P></P><OLTYPE="1"><LI><P>The method '-getDoubleSample' was redefined to useonly double variables in its implementation (instead of long doubles).</P></LI><LI><P>The macros used for starting seed generation werechanged to avoid a situation where many new generators would be createdthe same starting seed (if '--varyseed' was not specified.) See theGenerator Usage Guide and the Reference Guide for details.</P></LI></OL> </P></DIV><DIVCLASS="FORMALPARA"><P><B>Version 0.7: Improvements over version 0.6. </B><P></P><UL><LI><P>A host of new generators, located on the web or in theliterature, have been added since the last version of Random. There isnow a total of 36 different generators defined! Some of these haveimmense periods, some are very fast, and some have much betterstatistical properties than the old generators.</P></LI><LI><P>A new *type* of generator, the `split' generator, hasbeen introduced in the form of L'Ecuyer's C2LCGXgen and C4LCGXgengenerators.</P></LI><LI⌨️ 快捷键说明
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