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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML3.2 EN">
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<HEAD> <link rel="canonical" href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecNorm.html" />
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<TITLE>VecNorm</TITLE>
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<BODY BGCOLOR="FFFFFF">
<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
<div id="bugreport" align=right><a href="mailto:petsc-maint@mcs.anl.gov?subject=Typo or Error in Documentation &body=Please describe the typo or error in the documentation: petsc-3.7.5 v3.7.5 docs/manualpages/Vec/VecNorm.html "><small>Report Typos and Errors</small></a></div>
<A NAME="VecNorm"><H1>VecNorm</H1></A>
Computes the vector norm.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscvec.h"
PetscErrorCode VecNorm(Vec x,NormType type,PetscReal *val)
</PRE>
Collective on <A HREF="../Vec/Vec.html#Vec">Vec</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>x </B></TD><TD>- the vector
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>type </B></TD><TD>- one of <A HREF="../Vec/NORM_1.html#NORM_1">NORM_1</A>, <A HREF="../Vec/NORM_2.html#NORM_2">NORM_2</A>, <A HREF="../Vec/NORM_INFINITY.html#NORM_INFINITY">NORM_INFINITY</A>. Also available
<A HREF="../Vec/NORM_1_AND_2.html#NORM_1_AND_2">NORM_1_AND_2</A>, which computes both norms and stores them
in a two element array.
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameter</FONT></H3>
<DT><B>val </B> -the norm
<br>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
<pre>
<A HREF="../Vec/NORM_1.html#NORM_1">NORM_1</A> denotes sum_i |x_i|
</pre>
<pre>
<A HREF="../Vec/NORM_2.html#NORM_2">NORM_2</A> denotes sqrt(sum_i (x_i)^2)
</pre>
<pre>
<A HREF="../Vec/NORM_INFINITY.html#NORM_INFINITY">NORM_INFINITY</A> denotes max_i |x_i|
</pre>
<P>
For complex numbers <A HREF="../Vec/NORM_1.html#NORM_1">NORM_1</A> will return the traditional 1 norm of the 2 norm of the complex numbers; that is the 1
norm of the absolutely values of the complex entries. In PETSc 3.6 and earlier releases it returned the 1 norm of
the 1 norm of the complex entries (what is returned by the BLAS routine asum()). Both are valid norms but most
people expect the former.
<P>
<P>
<H3><FONT COLOR="#CC3333">Performance Issues</FONT></H3>
<pre>
per-processor memory bandwidth
</pre>
<pre>
interprocessor latency
</pre>
<pre>
work load inbalance that causes certain processes to arrive much earlier than others
</pre>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Vec/VecDot.html#VecDot">VecDot</A>(), <A HREF="../Vec/VecTDot.html#VecTDot">VecTDot</A>(), <A HREF="../Vec/VecNorm.html#VecNorm">VecNorm</A>(), <A HREF="../Vec/VecDotBegin.html#VecDotBegin">VecDotBegin</A>(), <A HREF="../Vec/VecDotEnd.html#VecDotEnd">VecDotEnd</A>(), <A HREF="../Vec/VecNormAvailable.html#VecNormAvailable">VecNormAvailable</A>(),
<BR><A HREF="../Vec/VecNormBegin.html#VecNormBegin">VecNormBegin</A>(), <A HREF="../Vec/VecNormEnd.html#VecNormEnd">VecNormEnd</A>()
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/vec/vec/interface/rvector.c.html#VecNorm">src/vec/vec/interface/rvector.c</A>
<BR><A HREF="./index.html">Index of all Vec routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/vec/vec/examples/tutorials/ex1.c.html">src/vec/vec/examples/tutorials/ex1.c.html</A><BR>
<A HREF="../../../src/vec/vec/examples/tutorials/ex11.c.html">src/vec/vec/examples/tutorials/ex11.c.html</A><BR>
<A HREF="../../../src/vec/vec/examples/tutorials/ex1f.F.html">src/vec/vec/examples/tutorials/ex1f.F.html</A><BR>
<A HREF="../../../src/vec/vec/examples/tutorials/ex1f90.F.html">src/vec/vec/examples/tutorials/ex1f90.F.html</A><BR>
<A HREF="../../../src/vec/vec/examples/tutorials/ex11f.F.html">src/vec/vec/examples/tutorials/ex11f.F.html</A><BR>
<A HREF="../../../src/vec/vec/examples/tutorials/ex20f90.F90.html">src/vec/vec/examples/tutorials/ex20f90.F90.html</A><BR>
<A HREF="../../../src/mat/examples/tutorials/ex2.c.html">src/mat/examples/tutorials/ex2.c.html</A><BR>
<A HREF="../../../src/mat/examples/tutorials/ex9.c.html">src/mat/examples/tutorials/ex9.c.html</A><BR>
<A HREF="../../../src/dm/examples/tutorials/ex10.c.html">src/dm/examples/tutorials/ex10.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex1.c.html">src/ksp/ksp/examples/tutorials/ex1.c.html</A><BR>
<A HREF="../../../src/ksp/ksp/examples/tutorials/ex2.c.html">src/ksp/ksp/examples/tutorials/ex2.c.html</A><BR>
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