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It is provided "as is" without express or implied warranty. -- --><Head><Title>inner_product</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>inner_product</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: algorithms</TD><TD Align=right VAlign=top><b>Component type</b>: function</TD></TR></Table><h3>Prototype</h3><tt>Inner_product</tt> is an overloaded name; there are actually two<tt>inner_product</tt> functions.<pre>template <class <A href="InputIterator.html">InputIterator</A>1, class <A href="InputIterator.html">InputIterator</A>2, class T>T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init);template <class <A href="InputIterator.html">InputIterator</A>1, class <A href="InputIterator.html">InputIterator</A>2, class T, class <A href="BinaryFunction.html">BinaryFunction</A>1, class <A href="BinaryFunction.html">BinaryFunction</A>2>T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init, BinaryFunction1 binary_op1, BinaryFunction2 binary_op2);</pre> <h3>Description</h3><tt>Inner_product</tt> calculates a generalized inner product of the ranges<tt>[first1, last1)</tt> and <tt>[first2, last2)</tt>.<P>The first version of <tt>inner_product</tt> returns<tt>init</tt> plus the inner product of the two ranges <A href="#1">[1]</A>. That is,it first initializes the result to <tt>init</tt> and then, for each iterator<tt>i</tt> in <tt>[first1, last1)</tt>, in order from the beginning to the end of the range, updates the result by <tt>result = result + (*i)* *(first2 + (i - first1))</tt>. <P>The second version of <tt>inner_product</tt> is identical to the first, exceptthat it uses two user-supplied <A href="functors.html">function objects</A> instead of <tt>operator+</tt> and <tt>operator*</tt>. That is, it first initializes the result to <tt>init</tt> and then, for each iterator<tt>i</tt> in <tt>[first1, last1)</tt>, in order from the beginning to the end of the range, updates the result by <tt>result = binary_op1(result, binary_op2(*i, *(first2 + (i - first1)))</tt>. <A href="#2">[2]</A><h3>Definition</h3>Defined in the standard header <A href="numeric">numeric</A>, and in the nonstandardbackward-compatibility header <A href="algo.h">algo.h</A>.<h3>Requirements on types</h3>For the first version:<UL><LI><tt>InputIterator1</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>InputIterator2</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>T</tt> is a model of <A href="Assignable.html">Assignable</A>.<LI>If <tt>x</tt> is an object of type <tt>T</tt>, <tt>y</tt> is an object of <tt>InputIterator1</tt>'s value type, and <tt>z</tt> is an object of <tt>InputIterator2</tt>'s value type, then <tt>x + y * z</tt> is defined.<LI>The type of <tt>x + y * z</tt> is convertible to <tt>T</tt>.</UL>For the second version:<UL><LI><tt>InputIterator1</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>InputIterator2</tt> is a model of <A href="InputIterator.html">Input Iterator</A>.<LI><tt>T</tt> is a model of <A href="Assignable.html">Assignable</A>.<LI><tt>BinaryFunction1</tt> is a model of <A href="BinaryFunction.html">Binary Function</A>.<LI><tt>BinaryFunction2</tt> is a model of <A href="BinaryFunction.html">Binary Function</A>.<LI><tt>InputIterator1</tt>'s value type is convertible to <tt>BinaryFunction2</tt>'s first argument type.<LI><tt>InputIterator2</tt>'s value type is convertible to <tt>BinaryFunction2</tt>'s second argument type.<LI><tt>T</tt> is convertible to <tt>BinaryFunction1</tt>'s first argument type.<LI><tt>BinaryFunction2</tt>'s return type is convertible to <tt>BinaryFunction1</tt>'s second argument type.<LI><tt>BinaryFunction1</tt>'s return type is convertible to <tt>T</tt>.</UL><h3>Preconditions</h3><UL><LI><tt>[first1, last1)</tt> is a valid range.<LI><tt>[first2, first2 + (last1 - first1))</tt> is a valid range.</UL><h3>Complexity</h3>Linear. Exactly <tt>last1 - first1</tt> applications of each binary operation.<h3>Example</h3><pre>int main(){ int A1[] = {1, 2, 3}; int A2[] = {4, 1, -2}; const int N1 = sizeof(A1) / sizeof(int); cout << "The inner product of A1 and A2 is " << inner_product(A1, A1 + N1, A2, 0) << endl;}</pre><h3>Notes</h3><P><A name="1">[1]</A>There are several reasons why it is important that <tt>inner_product</tt>starts with the value <tt>init</tt>. One of the most basic is that this allows<tt>inner_product</tt> to have a well-defined result even if <tt>[first1, last1)</tt> isan empty range: if it is empty, the return value is <tt>init</tt>.The ordinary inner product corresponds to setting <tt>init</tt> to 0.<P><A name="2">[2]</A>Neither binary operation is required to be either associative orcommutative: the order of all operations is specified.<h3>See also</h3><tt><A href="accumulate.html">accumulate</A></tt>, <tt><A href="partial_sum.html">partial_sum</A></tt>, <tt><A href="adjacent_difference.html">adjacent_difference</A></tt>,<tt><A href="count.html">count</A></tt><!-- 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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