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Difference between revisions of "Contraction(2)"

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An affine transformation of the plane under which each point is shifted towards the <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258201.png" />-axis, parallel to the <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258202.png" />-axis, by a distance proportional to its ordinate. In a Cartesian coordinate system a contraction is given by the relations
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An affine transformation of the plane under which each point is shifted towards the x-axis, parallel to the y-axis, by a distance proportional to its ordinate. In a Cartesian coordinate system a contraction is given by the relations
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258203.png" /></td> </tr></table>
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$$x'=x,\quad y'=ky,\quad k>0.$$
  
A contraction of space towards the <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258204.png" />-plane, parallel to the <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258205.png" />-axis, is given by the relations
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A contraction of space towards the $xy$-plane, parallel to the $z$-axis, is given by the relations
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025820/c0258206.png" /></td> </tr></table>
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$$x'=x,\quad y'=y,\quad z'=kz,\quad k>0.$$
  
  

Latest revision as of 07:14, 23 August 2014

An affine transformation of the plane under which each point is shifted towards the x-axis, parallel to the y-axis, by a distance proportional to its ordinate. In a Cartesian coordinate system a contraction is given by the relations

$$x'=x,\quad y'=ky,\quad k>0.$$

A contraction of space towards the $xy$-plane, parallel to the $z$-axis, is given by the relations

$$x'=x,\quad y'=y,\quad z'=kz,\quad k>0.$$


Comments

More usually, a contraction is defined as a transformation of a metric space that reduces distances. The notion defined above has no established name in Western literature, but is sometimes called a compression or compression-expansion.

How to Cite This Entry:
Contraction(2). Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Contraction(2)&oldid=15206
This article was adapted from an original article by N.V. Reveryuk (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article