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extern/stdcxx/4.2.1/doc/stdlibref/inner-product.html
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<HTML>
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<HEAD>
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<TITLE>inner_product()</TITLE>
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<LINK REL=StyleSheet HREF="../rw.css" TYPE="text/css" TITLE="Apache stdcxx Stylesheet"></HEAD>
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<BODY BGCOLOR=#FFFFFF>
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<A HREF="indirect-array.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="inplace-merge.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
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<H2>inner_product()</H2>
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<P><B>Library:</B> <A HREF="2-10.html">Numerics</A></P>
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<PRE><HR><B><I>Function</I></B><HR></PRE>
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<UL>
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<LI><A HREF="#sec1">Local Index</A></LI>
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<LI><A HREF="#sec2">Summary</A></LI>
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<LI><A HREF="#sec3">Synopsis</A></LI>
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<LI><A HREF="#sec4">Description</A></LI>
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<LI><A HREF="#sec5">Complexity</A></LI>
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<LI><A HREF="#sec6">Example</A></LI>
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<LI><A HREF="#sec7">Standards Conformance</A></LI>
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</UL>
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<A NAME="sec1"><H3>Local Index</H3></A>
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No Entries
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<A NAME="sec2"><H3>Summary</H3></A>
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<P>A generalized numeric operation that computes the inner product <SAMP>A X B</SAMP> of two ranges <SAMP>A</SAMP> and <SAMP>B</SAMP></P>
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<A NAME="sec3"><H3>Synopsis</H3></A>
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<PRE>#include <numeric>
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namespace std {
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template <class InputIterator1, class InputIterator2,
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class T>
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T inner_product(InputIterator1 start1,
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InputIterator1 finish1,
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InputIterator2 start2, T init);
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template <class InputIterator1, class InputIterator2,
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class T,
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class BinaryOperation1,
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class BinaryOperation2>
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T inner_product(InputIterator1 start1,
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InputIterator1 finish1,
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InputIterator2 start2, T init,
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BinaryOperation1 binary_op1,
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BinaryOperation2 binary_op2);
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}
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</PRE>
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<A NAME="sec4"><H3>Description</H3></A>
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<P>There are two versions of <SAMP>inner_product()</SAMP>. The first computes an inner product using the default multiplication and addition operators, while the second allows you to specify binary operations to use in place of the default operations. </P>
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<P>The first version of the function initializes <SAMP>acc</SAMP> with <SAMP>init</SAMP> and then modifies it with:</P>
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<P><SAMP>acc = acc + ((*i1) * (*i2))</SAMP></P>
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<P>for every iterator <SAMP>i1</SAMP> in the range <SAMP>[start1, finish1)</SAMP> and iterator <SAMP>i2</SAMP> in the range <SAMP>[start2, start2 + (finish1 - start1))</SAMP>. The algorithm returns <SAMP>acc</SAMP>.</P>
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<P>The second version of the function initializes <SAMP>acc</SAMP> with <SAMP>init</SAMP>, then computes:</P>
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<P><SAMP>acc = binary_op1(acc, binary_op2(*i1, *i2))</SAMP></P>
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<P>for every iterator <SAMP>i1</SAMP> in the range <SAMP>[start1, finish1)</SAMP> and iterator <SAMP>i2</SAMP> in the range <SAMP>[start2, start2 + (finish1 - start1))</SAMP>.</P>
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<A NAME="sec5"><H3>Complexity</H3></A>
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<P>The <SAMP>inner_product()</SAMP> algorithm computes exactly <SAMP>(finish1 - start1)</SAMP> applications of either:</P>
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<P><SAMP>acc + (*i1) * (*i2)</SAMP></P>
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<P> or </P>
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<P><SAMP>binary_op1(acc, binary_op2(*i1, *i2)).</SAMP></P>
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<A NAME="sec6"><H3>Example</H3></A>
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<UL><PRE>//
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// inr_prod.cpp
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//
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#include <algorithm> // for copy
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#include <numeric> // for inner_product
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#include <iostream> // for cout, endl
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#include <list> // for list
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#include <vector> // for vector
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#include <functional> // for plus, minus
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int main ()
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{
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typedef std::list<int, std::allocator<int> > List;
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typedef std::vector<int, std::allocator<int> > Vector;
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typedef std::ostream_iterator<int, char,
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std::char_traits<char> > os_iter;
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// Initialize a list and a vector using arrays of ints.
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int a1[] = { 6, -3, -2 };
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int a2[] = { -2, -3, -2 };
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List l (a1, a1 + sizeof a1 / sizeof *a1);
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Vector v (a2, a2 + sizeof a2 / sizeof *a2);
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// Calculate the inner product of the two sets of values.
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List::value_type prod = std::inner_product (l.begin (),
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l.end (), v.begin (), 0);
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// Calculate a wacky inner product using the same values.
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List::value_type wacky =
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std::inner_product (l.begin (), l.end (), v.begin (),
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0, std::plus<List::value_type>(),
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std::minus<List::value_type>());
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// Print the output.
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std::cout << "For the sets of numbers: { ";
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std::copy (v.begin (), v.end (), os_iter (std::cout, " "));
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std::cout << "} and { ";
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std::copy (l.begin (), l.end (), os_iter (std::cout, " "));
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std::cout << "}\nThe inner product is: " << prod
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<< "\nThe wacky result is: " << wacky
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<< std::endl;
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return 0;
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}
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Program Output:
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For the sets of numbers: { -2 -3 -2 } and { 6 -3 -2 }
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The inner product is: 1
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The wacky result is: 8
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</PRE></UL>
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<UL><PRE></PRE></UL>
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<A NAME="sec7"><H3>Standards Conformance</H3></A>
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<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 26.4.2</I></P>
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