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### 5.1.2 Lines

`BSpline (`

`expression`) = {`expression-list`};Creates a B-spline curve. The

`expression`inside the parentheses is the B-spline curve’s identification number; the`expression-list`on the right hand side should contain the identification numbers of all the B-spline’s control points. Repeating control points has the expected effect.`Circle (`

`expression`) = {`expression`,`expression`,`expression`};Creates a circle arc (strictly) smaller than Pi. The

`expression`inside the parentheses is the circle arc’s identification number; the first`expression`inside the braces on the right hand side gives the identification number of the start point of the arc; the second`expression`gives the identification number of the center of the circle; the last`expression`gives the identification number of the end point of the arc.`CatmullRom (`

`expression`) = {`expression-list`};`CatmullRom`

is a synonym for`Spline`

.`Ellipse (`

`expression`) = {`expression`,`expression`,`expression`,`expression`};Creates an ellipse arc. The

`expression`inside the parentheses is the ellipse arc’s identification number; the first`expression`inside the braces on the right hand side gives the identification number of the start point of the arc; the second`expression`gives the identification number of the center of the ellipse; the third`expression`gives the identification number of any point located on the major axis of the ellipse; the last`expression`gives the identification number of the end point of the arc.`Line (`

`expression`) = {`expression`,`expression`};Creates a straight line segment. The

`expression`inside the parentheses is the line segment’s identification number; the two`expression`s inside the braces on the right hand side give identification numbers of the start and end points of the segment.`Spline (`

`expression`) = {`expression-list`};Creates a spline curve. The

`expression`inside the parentheses is the spline’s identification number; the`expression-list`on the right hand side should contain the identification numbers of all the spline’s control points.`Line Loop (`

`expression`) = {`expression-list`};Creates an oriented line loop. The

`expression`inside the parentheses is the line loop’s identification number; the`expression-list`on the right hand side should contain the identification numbers of all the elementary lines that constitute the line loop. A line loop must be a closed loop, and the elementary lines should be ordered and oriented (using negative identification numbers to specify reverse orientation). If the orientation is correct, but the ordering is wrong, Gmsh will actually reorder the list internally to create a consistent loop. Although Gmsh supports it, it is not recommended to specify multiple line loops (or subloops) in a single`Line Loop`

command. (Line loops are used to create surfaces: see Surfaces.)`Compound Line (`

`expression`) = {`expression-list`};Creates a compound line from several elementary lines. When meshed, a compound line will be reparametrized as a single line, whose mesh can thus cross internal boundaries. The

`expression`inside the parentheses is the compound line’s identification number; the`expression-list`on the right hand side contains the identification number of the elementary lines that should be reparametrized as a single line. See`Compound Surface`

for additional information on compound entities.`Physical Line (`

`expression`|`char-expression`) = {`expression-list`};Creates a physical line. The

`expression`inside the parentheses is the physical line’s identification number (if a`char-expression`is given instead, a unique identification number is automatically created); the`expression-list`on the right hand side should contain the identification numbers of all the elementary lines that need to be grouped inside the physical line. Specifying negative identification numbers in the`expression-list`will reverse the orientation of the mesh elements belonging to the corresponding elementary lines in the saved mesh.

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