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It is provided "as is" without express or implied warranty. -- --><Head><Title>subtractive_rng</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--end header--><BR Clear><H1>subtractive_rng</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "functors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: functors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3><tt>Subtractive_rng</tt> is a <A href="RandomNumberGenerator.html">Random Number Generator</A> based on thesubtractive method <A href="#1">[1]</A>. It is a <A href="UnaryFunction.html">Unary Function</A>: it takesa single argument <tt>N</tt>, an <tt>unsigned int</tt>, and returns an <tt>unsigned int</tt> that is less than <tt>N</tt>. Successive calls tothe same <tt>subtractive_rng</tt> object <A href="#2">[2]</A> yield a pseudo-randomsequence.<h3>Example</h3><pre>int main(){ subtractive_rng R; for (int i = 0; i < 20; ++i) cout << R(5) << ' '; cout << endl;}// The output is 3 2 3 2 4 3 1 1 2 2 0 3 4 4 4 4 2 1 0 0 </pre><h3>Definition</h3>Defined in the standard header <A href="functional">functional</A>, and in the nonstandardbackward-compatibility header <A href="function.h">function.h</A>.This function object is an SGI extension; it is not part of the C++standard.<h3>Template parameters</h3>None.<h3>Model of</h3><A href="RandomNumberGenerator.html">Random Number Generator</A>, <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><h3>Type requirements</h3>None.<h3>Public base classes</h3><tt><A href="unary_function.html">unary_function</A><unsigned int, unsigned int></tt><h3>Members</h3><Table border><TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR><TR><TD VAlign=top><tt>argument_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of a <tt>subtractive_rng</tt>'s argument: <tt>unsigned int</tt>.</TD></TR><TR><TD VAlign=top><tt>result_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of the result: <tt>unsigned int</tt>.</TD></TR><TR><TD VAlign=top><tt>subtractive_rng(unsigned int seed)</tt></TD><TD VAlign=top><tt>subtractive_rng</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>subtractive_rng()</tt></TD><TD VAlign=top><tt>subtractive_rng</tt></TD><TD VAlign=top>See below.</TD></TR><TR><TD VAlign=top><tt>unsigned int operator()(unsigned int N)</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>Function call. Returns a pseudo-random number in the range <tt>[0, N)</tt>.</TD></TR><TR><TD VAlign=top><tt>void initialize(unsigned int seed)</tt></TD><TD VAlign=top><tt>subtractive_rng</tt></TD><TD VAlign=top>See below.</TD></tr></table><h3>New members</h3>These members are not defined in the <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A>requirements, but are specific to <tt>subtractive_rng</tt>.<Table border><TR><TH>Member</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>subtractive_rng(unsigned int seed)</tt></TD><TD VAlign=top>The constructor. Creates a <tt>subtractive_rng</tt> whose internal state is initialized using <tt>seed</tt>.</TD></TR><TR><TD VAlign=top><tt>subtractive_rng()</tt></TD><TD VAlign=top>The default constructor. Creates a <tt>subtractive_rng</tt> initialized using a default value.</TD></TR><TR><TD VAlign=top><tt>void initialize(unsigned int seed)</tt></TD><TD VAlign=top>Re-initializes the internal state of the <tt>subtractive_rng</tt>, using the value <tt>seed</tt>.</TD></tr></table><h3>Notes</h3><P><A name="1">[1]</A>See section 3.6 of Knuth for an implementation of the subtractivemethod in FORTRAN. Section 3.2.2 of Knuth analyzes this class ofalgorithms.(D. E. Knuth, <i>The Art of ComputerProgramming. Volume 2: Seminumerical Algorithms</i>, second edition. Addison-Wesley, 1981.)<P><A name="2">[2]</A>Note that the sequence produced by a <tt>subtractive_rng</tt> iscompletely deterministic, and that the sequences produced by twodifferent <tt>subtractive_rng</tt> objects are independent of each other.That is: if <tt>R1</tt> is a <tt>subtractive_rng</tt>, then the values returned when<tt>R1</tt> is called depend only on <tt>R1</tt>'s seed and on the number of timesthat <tt>R1</tt> has been called. Calls to other <tt>subtractive_rng</tt> objectsare irrelevant. In implementation terms, this is because the class<tt>subtractive_rng</tt> contains no <tt>static</tt> members.<h3>See also</h3><A href="RandomNumberGenerator.html">Random Number Generator</A><!-- start footer --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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