[Gmsh] Line of multiple segments
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Mon Sep 21 17:49:36 CEST 2009
Geordie McBain wrote:
> I just noticed that the Line command accepts more than two points. In fact, it behaves like BSpline and Spline and accepts an expression-list. This behaviour is quite useful in my application, but is undocumented (S. 5.1.2 `Lines' <http://geuz.org/gmsh/doc/texinfo/gmsh.html#Lines>). Should and may I rely on this behaviour?
> The behaviour is useful because I only need one line command for each chain of line segments, and because it applies a single identifier to the whole chain it is much easier to refer to the chain later, e.g. in the Line Loop and Physical Line commands. It's also useful because I can simply swap Line, Spline, and BSpline in the input file without any other modification. I attach three examples, differing only in this command.
> If the behaviour is intended and may be relied on, perhaps the documentation for Line could be amended to read something like:
You can fairly safely use lines with multiple segments in 2D, but they
are not supported in 3D (e.g. extruding a "multi-line" will lead to
unexpected results). We chose not to document the feature for this reason...
>
> %<---OLD
> Line ( expression ) = { expression, expression };
> Creates a straight line segment. The expression inside the parentheses is the line segment's identification number; the two expressions inside the braces on the right hand side give identification numbers of the start and end points of the segment.
> %<---PROPOSED
> Line ( expresison ) = { expression-list };
> Creates a polygonal line. The expression inside the parenthesis is the polygonal line's identification number; the expression-list on the right hand side should contain the identification numbers of all the polygonal line's vertices.
> %<---END
>
>
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--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine