Luigi Pasinetti: Difference between revisions
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In [[geometry]], the '''semidiameter''' or '''semi-diameter''' of a [[set (mathematics)|set]] of [[point (geometry)|point]]s may be one half of its [[diameter]]; or, sometimes, one half of its extent along a particular direction. | |||
==Special cases== | |||
The semi-diameter of a [[sphere]], [[circle]], or [[interval (mathematics)|interval]] is the same thing as its [[radius (geometry)|radius]] — namely, any [[line segment]] from the [[Center (algebra)|center]] to its [[boundary (topology)|boundary]]. | |||
The semi-diameters of a non-circular [[ellipse]] are the halves of its extents along the two [[axis of symmetry|axes of symmetry]]. They are the parameters ''a'', ''b'' of the [[implicit function|implicit equation]] | |||
:<math>\left(\frac{x}{a}\right)^{2}+\left(\frac{y}{b}\right)^{2}=1;\,\!</math> | |||
Likewise, the semi-diameters of an [[ellipsoid]] are the parameters ''a'', ''b'', and ''c'' of its implicit equation | |||
:<math>\left(\frac{x}{a}\right)^{2}+\left(\frac{y}{b}\right)^{2}+\left(\frac{z}{c}\right)^{2}=1;\,\!</math> | |||
The semi-diameters of a [[superellipse]], [[superellipsoid]], or [[superquadric]] can be identified in the same way. | |||
[[Category:Geometric measurement]] |
Revision as of 11:30, 22 July 2013
In geometry, the semidiameter or semi-diameter of a set of points may be one half of its diameter; or, sometimes, one half of its extent along a particular direction.
Special cases
The semi-diameter of a sphere, circle, or interval is the same thing as its radius — namely, any line segment from the center to its boundary.
The semi-diameters of a non-circular ellipse are the halves of its extents along the two axes of symmetry. They are the parameters a, b of the implicit equation
Likewise, the semi-diameters of an ellipsoid are the parameters a, b, and c of its implicit equation
The semi-diameters of a superellipse, superellipsoid, or superquadric can be identified in the same way.