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<!DOCTYPE document PUBLIC "-//CNX//DTD CNXML 0.5 plus MathML//EN" "http://cnx.rice.edu/cnxml/0.5/DTD/cnxml_mathml.dtd">
<document xmlns="http://cnx.rice.edu/cnxml" xmlns:m="http://www.w3.org/1998/Math/MathML" xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns:bib="http://bibtexml.sf.net/" id="m10437">
  
  <name>The Haar System as an Example of DWT</name>
  <metadata>
  <md:version>2.10</md:version>
  <md:created>2002/01/07</md:created>
  <md:revised>2005/10/05 15:28:46.647 GMT-5</md:revised>
  <md:authorlist>
      <md:author id="schniter">
      <md:firstname>Phil</md:firstname>
      
      <md:surname>Schniter</md:surname>
      <md:email>schniter@ee.eng.ohio-state.edu</md:email>
    </md:author>
  </md:authorlist>

  <md:maintainerlist>
    <md:maintainer id="charlet">
      <md:firstname>Charlet</md:firstname>
      
      <md:surname>Reedstrom</md:surname>
      <md:email>charlet@rice.edu</md:email>
    </md:maintainer>
    <md:maintainer id="schniter">
      <md:firstname>Phil</md:firstname>
      
      <md:surname>Schniter</md:surname>
      <md:email>schniter@ee.eng.ohio-state.edu</md:email>
    </md:maintainer>
  </md:maintainerlist>
  
  <md:keywordlist>
    <md:keyword>Discrete Wavelet Transform</md:keyword>
    <md:keyword>Haar</md:keyword>
    <md:keyword>scaling function</md:keyword>
    <md:keyword>wavelet</md:keyword>
  </md:keywordlist>

  <md:abstract>(Blank Abstract)</md:abstract>
</metadata>

  <content>
    <para id="haar1">
      The Haar basis is perhaps the simplest example of a DWT basis,
      and we will frequently refer to it in our DWT development.
      Keep in mind, however, that <emphasis>the Haar basis is only
	an example</emphasis>; there are many other ways of
      constructing a DWT decomposition.
    </para>

    <para id="haar2">
      For the Haar case, the mother <term>scaling function</term> is
      defined by <cnxn target="haareq1" strength="9"/> and <cnxn target="sqscalingfn" strength="9"/>.

      <equation id="haareq1">
	<m:math display="block">
	  <m:apply>
	    <m:eq/>
	    <m:apply>
	      <m:ci type="fn">φ</m:ci>
	      <m:ci>t</m:ci>
	    </m:apply>
	    <m:piecewise>
	      <m:piece>
		<m:cn>1</m:cn>
		<m:apply>
		  <m:leq/>
		  <m:cn>0</m:cn>
		  <m:apply>
		    <m:lt/>
		    <m:ci>t</m:ci>
		    <m:cn>1</m:cn>
		  </m:apply>
		</m:apply>
	      </m:piece>
	      <m:otherwise>
		<m:cn>0</m:cn>
	      </m:otherwise>
	    </m:piecewise>
	  </m:apply>
	</m:math>
      </equation>
    </para>

    <figure id="sqscalingfn">
      <media type="image/png" src="scalingfn.png"/>
    </figure>

    <para id="closure">
      From the mother scaling function, we define a family of
      shifted and stretched scaling functions
      <m:math>
	<m:set>
	  <m:apply>
	    <m:ci type="fn"><m:msub>
		<m:mi>φ</m:mi>
		<m:mrow>
		  <m:mi>k</m:mi>
		  <m:mo>,</m:mo>
		  <m:mi>n</m:mi>
		</m:mrow>
	      </m:msub></m:ci>
	    <m:ci>t</m:ci>
	  </m:apply>
	</m:set>
      </m:math> according to <cnxn target="haareq2" strength="9"/> and
      <cnxn target="shandstr" strength="9"/>
      
      <equation id="haareq2">
	<m:math>
	  <m:apply>
	    <m:eq/>
	    <m:apply>
	      <m:ci type="fn"><m:msub>
		  <m:mi>φ</m:mi>
		  <m:mrow>
		    <m:mi>k</m:mi>
		    <m:mo>,</m:mo>
		    <m:mi>n</m:mi>
		  </m:mrow>
		</m:msub></m:ci>
	      <m:ci>t</m:ci>
	    </m:apply>
	    <m:apply>
	      <m:forall/>
	      <m:bvar><m:ci>k</m:ci></m:bvar>
	      <m:bvar><m:ci>n</m:ci></m:bvar>
	      <m:condition>
		<m:apply>
		  <m:in/>
		  <m:ci>k</m:ci>
		  <m:integers/>
		</m:apply>
	      </m:condition>
	      <m:condition>
		<m:apply>
		  <m:in/>
		  <m:ci>n</m:ci>
		  <m:integers/>
		</m:apply>
	      </m:condition>
	      <m:apply>
		<m:times/>
		<m:apply>
		  <m:power/>
		  <m:cn>2</m:cn>
		  <m:apply>
		    <m:minus/>
		    <m:apply>
		      <m:divide/>
		      <m:ci>k</m:ci>
		      <m:cn>2</m:cn>
		    </m:apply>
		  </m:apply>
		</m:apply>
		<m:apply>
		  <m:ci type="fn">φ</m:ci>
		  <m:apply>
		    <m:minus/>
		    <m:apply>
		      <m:times/>
		      <m:apply>
			<m:power/>
			<m:cn>2</m:cn>
			<m:apply>
			  <m:minus/>
			  <m:ci>k</m:ci>
			</m:apply>
		      </m:apply>
		      <m:ci>t</m:ci>
		    </m:apply>
		    <m:ci>n</m:ci>
		  </m:apply>
		</m:apply>
	      </m:apply>
	    </m:apply>

	    <m:apply>
	      <m:times/>
	      <m:apply>
		<m:power/>
		<m:cn>2</m:cn>
		<m:apply>
		  <m:minus/>
		  <m:apply>
		    <m:divide/>
		    <m:ci>k</m:ci>
		    <m:cn>2</m:cn>
		  </m:apply>
		</m:apply>
	      </m:apply>
	      <m:apply>
		<m:ci type="fn">φ</m:ci>
		<m:apply>
		  <m:times/>
		  <m:apply>
		    <m:divide/>
		    <m:cn>1</m:cn>
		    <m:apply>
		      <m:power/>
		      <m:cn>2</m:cn>
		      <m:ci>k</m:ci>
		    </m:apply>
		  </m:apply>
		  <m:apply>
		    <m:minus/>
		    <m:ci>t</m:ci>
		    <m:apply>
		      <m:times/>
		      <m:ci>n</m:ci>
		      <m:apply>
			<m:power/>
			<m:cn>2</m:cn>
			<m:ci>k</m:ci>
		      </m:apply>
		    </m:apply>
		  </m:apply>
		</m:apply>
	      </m:apply>
	    </m:apply>
	  </m:apply>
	</m:math>
      </equation>
    </para>

    <figure id="shandstr">
      <media type="image/png" src="shiftandstretchfn.png"/>
    </figure>

    <para id="haar3">
      which are illustrated in <cnxn target="fnrep" strength="9"/> for
      various <m:math><m:ci>k</m:ci></m:math> and
      <m:math><m:ci>n</m:ci></m:math>.  <cnxn target="haareq2" strength="9"/> makes clear the principle that incrementing
      <m:math><m:ci>n</m:ci></m:math> by one shifts the pulse one
      place to the right.  Observe from <cnxn target="fnrep" strength="9"/> that
      <m:math>
	<m:set>
	  <m:bvar>
	    <m:apply>
	      <m:ci type="fn"><m:msub>
		  <m:mi>φ</m:mi>
		  <m:mrow>
		    <m:mi>k</m:mi>
		    <m:mo>,</m:mo>
		    <m:mi>n</m:mi>
		  </m:mrow>
		</m:msub></m:ci>
	      <m:ci>t</m:ci>
	    </m:apply>
	  </m:bvar>
	  <m:condition>
	    <m:apply>
	      <m:in/>
	      <m:ci>n</m:ci>
	      <m:integers/>
	    </m:apply>
	  </m:condition>
	</m:set>
      </m:math>
      is orthonormal for each <m:math><m:ci>k</m:ci></m:math> (<foreign>i.e.</foreign>,
      along each row of figures).
    </para>

    <figure id="fnrep">
      <media type="image/png" src="haarscalingfn.png"/>
    </figure>

  </content>
</document>
