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	<title>Michi's blog &#187; Jahr der Mathematik</title>
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		<title>Algebraic surface toys!</title>
		<link>http://blog.mikael.johanssons.org/archive/2008/01/algebraic-surface-toys/</link>
		<comments>http://blog.mikael.johanssons.org/archive/2008/01/algebraic-surface-toys/#comments</comments>
		<pubDate>Fri, 25 Jan 2008 16:58:27 +0000</pubDate>
		<dc:creator>Michi</dc:creator>
				<category><![CDATA[Algebra]]></category>
		<category><![CDATA[Algebraic geometry]]></category>
		<category><![CDATA[Geometry]]></category>
		<category><![CDATA[Jahr der Mathematik]]></category>

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		<description><![CDATA[At the start of the German Year of Mathematics, the Oberwolfach research institute has released an exhibition and the software they used to produce it. The software, surfer, is a really nice GUI that sits on top of surf and lets you rotate and zoom your algebraic surfaces as well as pick colours very comfortably. [...]]]></description>
			<content:encoded><![CDATA[<p>At the start of the <a href=http://www.jahr-der-mathematik.de/>German Year of Mathematics</a>, the <a href=http://www.mfo.de>Oberwolfach research institute</a> has released an exhibition and the software they used to produce it. The software, <a href=http://imaginary2008.de/surfer.php>surfer</a>, is a really nice GUI that sits on top of <a href=http://surf.sourceforge.net>surf</a> and lets you rotate and zoom your algebraic surfaces as well as pick colours very comfortably.</p>
<p>They have a whole bunch of Really Pretty Images at <a href=http://imaginary2008.de>the exhibition website</a>, and I warmly recommend a visit. If you can get hold of the exhibition, they also have produced real models &#8211; with a 3d-printer &#8211; of some of the snazzier surfaces, so that one could have a REALLY close encounter with them.</p>
<p>But also, I&#8217;d really like to show you some of my own minor experiments with the program.</p>
<p><img src="http://mikael.johanssons.org/surfer/tubamirum.png" alt="Tuba Mirum - the innards of a Klein Bottle" width="75%" /><br />
This is the interior of a Klein Bottle, using the &#8220;standard&#8221; realization as an algebraic surface given by Mathworld. In other words, I&#8217;m using<br />
(x^2+y^2+z^2+2*y-1)*((x^2+y^2+z^2-2*y-1)^2-8*z^2)+16*x*z*(x^2+y^2+z^2-2*y-1)=0<br />
for the defining equation. It kinda looks a bit like a Sousaphone in my opinion.</p>
<p><img src="http://mikael.johanssons.org/surfer/roman.png" alt="Roman's surface - immersion of the real projective plane." width="75%" /><br />
Roman&#8217;s surface, an immersion of the real projective plane into 3-dimensional euclidean space. It is given by the equation<br />
(x^2+y^2+z^2-9)^2-((z-3)^2-2*x^2)*((z+3)^2-2*y^2)=0<br />
and is one of the Steiner projections of the Veronese surface, embedding the real projective plane into projective 5-dimensional space by the homogenous parametrization (x^2,y^2,z^2,xy,xz,yz).</p>
<p><img src="http://mikael.johanssons.org/surfer/steiner.png" alt="Steiner's surface type 2 - immersion of the real projective plane." width="75%" /><br />
With the defining equation<br />
x^2*y^2-x^2*z^2+y^2*z^2-x*y*z=0<br />
this Steiner surface can be transformed into the Roman surface above if (and only if) you&#8217;re allowed to take shortcuts over the points at infinity. As it is, it has two pinches (both visible) and three lines of self-intersections (also all visible, kinda sorta). It&#8217;s also unbounded &#8211; one of the reasons that you cannot get to the bounded Roman surface easily.</p>
<p>With this as inspiration &#8211; go forth and draw surfaces. And when you do, please show them to me too.</p>
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