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Update Pentagon.geo
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‎assets/advection_diffusion/Pentagon.geo‎

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// Gmsh project created on Wed Dec 4 14:27:19 2024
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// -----------------------------------------------------------------------------
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//
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// Gmsh GEO tutorial 1
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//
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// Geometry basics, elementary entities, physical groups
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//
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// -----------------------------------------------------------------------------
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// The simplest construction in Gmsh's scripting language is the
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// `affectation'. The following command defines a new variable `lc':
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lc = 1e-1;
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// This variable can then be used in the definition of Gmsh's simplest
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// `elementary entity', a `Point'. A Point is uniquely identified by a tag (a
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// strictly positive integer; here `1') and defined by a list of four numbers:
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// three coordinates (X, Y and Z) and the target mesh size (lc) close to the
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// point:
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// The distribution of the mesh element sizes will then be obtained by
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// interpolation of these mesh sizes throughout the geometry. Another method to
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// specify mesh sizes is to use general mesh size Fields (see `t10.geo'). A
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// particular case is the use of a background mesh (see `t7.geo').
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// If no target mesh size of provided, a default uniform coarse size will be
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// used for the model, based on the overall model size.
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// We can then define some additional points. All points should have different
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// tags:
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Point(1) = {0, -1.0000, 0, lc};
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Point(2) = {0, 1.0000, 0, lc};
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Point(3) = {1.9015, 1.6190, 0, lc};
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Point(4) = {3.0777, 0, 0, lc};
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Point(5) = {1.9015, -1.6190, 0, lc};
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// Point(1) = {0.8507, 0, 0, lc};
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// Point(2) = {0.2629, 0.8090, 0, lc};
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// Point(3) = {-0.6882, 0.5000, 0, lc};
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// Point(4) = {-0.6882, -0.5000, 0, lc};
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// Point(5) = {0.2629, -0.8090, 0, lc};
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// Curves are Gmsh's second type of elementary entities, and, amongst curves,
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// straight lines are the simplest. A straight line is identified by a tag and
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// is defined by a list of two point tags. In the commands below, for example,
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// the line 1 starts at point 1 and ends at point 2.
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//
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// Note that curve tags are separate from point tags - hence we can reuse tag
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// `1' for our first curve. And as a general rule, elementary entity tags in
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// Gmsh have to be unique per geometrical dimension.
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Line(1) = {1, 2};
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Line(2) = {2, 3};
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Line(3) = {3, 4};
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Line(4) = {4, 5};
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Line(5) = {5, 1};
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// The third elementary entity is the surface. In order to define a simple
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// rectangular surface from the four curves defined above, a curve loop has
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// first to be defined. A curve loop is also identified by a tag (unique amongst
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// curve loops) and defined by an ordered list of connected curves, a sign being
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// associated with each curve (depending on the orientation of the curve to form
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// a loop):
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Curve Loop(1) = {1, 2, 3, 4, 5};
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// We can then define the surface as a list of curve loops (only one here,
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// representing the external contour, since there are no holes--see `t4.geo' for
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// an example of a surface with a hole):
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Plane Surface(1) = {1};
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// At this level, Gmsh knows everything to display the rectangular surface 1 and
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// to mesh it. An optional step is needed if we want to group elementary
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// geometrical entities into more meaningful groups, e.g. to define some
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// mathematical ("domain", "boundary"), functional ("left wing", "fuselage") or
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// material ("steel", "carbon") properties.
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//
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// Such groups are called "Physical Groups" in Gmsh. By default, if physical
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// groups are defined, Gmsh will export in output files only mesh elements that
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// belong to at least one physical group. (To force Gmsh to save all elements,
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// whether they belong to physical groups or not, set `Mesh.SaveAll=1;', or
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// specify `-save_all' on the command line.) Physical groups are also identified
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// by tags, i.e. strictly positive integers, that should be unique per dimension
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// (0D, 1D, 2D or 3D). Physical groups can also be given names.
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//
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// Here we define a physical curve that groups the left, bottom and right curves
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// in a single group (with prescribed tag 5); and a physical surface with name
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// "My surface" (with an automatic tag) containing the geometrical surface 1:
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Physical Line("l1") = {1};
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Physical Line("l2") = {2};
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Physical Line("l3") = {3};
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Physical Surface("My surface") = {1};
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// Now that the geometry is complete, you can
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// - either open this file with Gmsh and select `2D' in the `Mesh' module to
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// create a mesh; then select `Save' to save it to disk in the default format
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// (or use `File->Export' to export in other formats);
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// - or run `gmsh t1.geo -2` to mesh in batch mode on the command line.
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// You could also uncomment the following lines in this script:
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//
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Mesh 2;
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Save "pentagon_mesh.msh";
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//
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// which would lead Gmsh to mesh and save the mesh every time the file is
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// parsed. (To simply parse the file from the command line, you can use `gmsh
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// t1.geo -')
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// By default, Gmsh saves meshes in the latest version of the Gmsh mesh file
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// format (the `MSH' format). You can save meshes in other mesh formats by
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// specifying a filename with a different extension in the GUI, on the command
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// line or in scripts. For example
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//
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// Save "t1.unv";
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//
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// will save the mesh in the UNV format. You can also save the mesh in older
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// versions of the MSH format:
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//
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// - In the GUI: open `File->Export', enter your `filename.msh' and then pick
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// the version in the dropdown menu.
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// - On the command line: use the `-format' option (e.g. `gmsh file.geo -format
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// msh2 -2').
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// - In a `.geo' script: add `Mesh.MshFileVersion = x.y;' for any version
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// number `x.y'.
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// - As an alternative method, you can also not specify the format explicitly,
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// and just choose a filename with the `.msh2' or `.msh4' extension.
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// Note that starting with Gmsh 3.0, models can be built using other geometry
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// kernels than the default built-in kernel. By specifying
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//
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// SetFactory("OpenCASCADE");
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//
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// any subsequent command in the `.geo' file would be handled by the OpenCASCADE
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// geometry kernel instead of the built-in kernel. Different geometry kernels
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// have different features. With OpenCASCADE, instead of defining the surface by
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// successively defining 4 points, 4 curves and 1 curve loop, one can define the
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// rectangular surface directly with
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//
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// Rectangle(2) = {.2, 0, 0, .1, .3};
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//
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// The underlying curves and points could be accessed with the `Boundary' or
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// `CombinedBoundary' operators.
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//
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// See e.g. `t16.geo', `t18.geo', `t19.geo' or `t20.geo' for complete examples
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// based on OpenCASCADE, and `examples/boolean' for more.

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