Talk:reflex

my husband has no reflex what do this mean — This unsigned comment was added by 71.160.217.57 (talk) at 05:51, 15 August 2008.

He's dead. Jonathan Webley 20:24, 15 August 2008 (UTC)

RFV discussion

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Rfv-sense: "Of an angle, greater than 180 degrees but less than 360 degrees". Is this ever used in any form besides the set phrase reflex angle? --EncycloPetey 03:17, 10 April 2010 (UTC)

Does that matter? (An overwhelmingly common usage is not the same as a set phrase.) The meaning of reflex is in the word reflex, demonstrated pretty well by “an angle is convex if it is not reflex.” —Michael Z. 2010-04-10 05:35 z

Please note that some of the added quotes (e.g. reflex edge, reflex vertices) do not apply to the single geometrical definition in the entry. Either the definition needs revision, or else some of these quotes pertain to other senses not yet defined. Also, the 1895 quote is defining the term, not using it, and so does not qualify under CFI. Only the 1878 and 2001 quotes look to support the current definition. --EncycloPetey 05:42, 10 April 2010 (UTC)

1895 is defining which term, reflex or reflex angle? —Michael Z. 2010-04-10 06:15 z

Why shouldn't 1958 (“the dihedral angle is reflex”) apply to the definition? —Michael Z. 2010-04-10 06:18 z

Because it's a three-dimensional quantity that is measured in a different way than a two-dimensional angle. --EncycloPetey 06:49, 10 April 2010 (UTC)

No, it's a simple two-dimensional angle between two three-dimensional surfaces, measured on the plane perpendicular to the edge where the surfaces meet (in this case, it's a reflex edge). —Michael Z. 2010-04-10 15:04 z

Perhaps the citations indicate a correct definition like “subtending greater than 180 degrees but less than 360 degrees of arc (usually, of an angle).” —Michael Z. 2010-04-10 06:23 z

That could work for just about everything except "reflex edge", but that might just be an aberrant usage. --EncycloPetey 06:49, 10 April 2010 (UTC)

Then “subtending greater than 180 degrees but less than 360 degrees of arc on a plane (usually, of an angle),” might work. That might be technically pedantic, since angles are normally measured thus. Reflex edge seems to be a normal phrase in 3-d geometry. —Michael Z. 2010-04-10 14:55 z

Another way to define this could be “of an angle, ... or having such an angle.” —Michael Z. 2010-04-10 15:40 z

• 1992[1]

  If the two faces form a local concavity (i.e. if their common edge is a reflex edge of the front) then they are likely to be part of the same tetrahedron.

• 1993[2]

  Here a reflex edge is defined as an edge e whose two adjacent faces lie on the same side of the vertical plane passing through e (this restricted definition of reflex edges excludes in practice most concave edges of free space and thus makes the system construct far fewer cells than would otherwise be required).

• 2007 [with diagram][3]

  The triangular base of the prism is twisted so that each of the three rectangular faces fold into two triangular faces with a reflex edge between them.

• 2008 [with diagram][4]

  Each of the three square faces is broken along a diagonal reflex edge (an edge at which the polyhedron is locally nonconvex) and two triangular faces.

2-d reflex edges:

• 2003[5]

  If P has no reflex edges, then P is cuttable by a circular saw, so any blueprint is valid.

Perhaps, but most of these seem to have to define what a reflex edge is. I'm more inclined to think that reflex edge deserves a separate entry with a 3-D definition, because the angle has to be "between two polyhedral faces with its vertex on the edge", rather than "an edge of a polygon where one (or both) of the angles with vertex at the segment's endpoints is reflex". --EncycloPetey 16:24, 10 April 2010 (UTC)

I cited those to illustrate the meaning of reflex, but I think they all use the term too, except arguably 1993. Maybe reflex edge could be defined, although it could also refer, e.g., to the interface of intersecting planes; it just happens that in problem-solving for modelling, etc., geometricians deal with polygons with common vertices. —Michael Z. 2010-04-10 16:48 z

RFV passed. —Ruakh_TALK 17:10, 4 September 2010 (UTC)