[Gmsh] Extrusion and outward normals to the whole surface

[Alexander Kalinin]

Dear Gmsh users,

I want to build a cylinder volume and I want to setup all normals to be
outward for the whole surface. I use the extrusion but the normals for the
first extruded surface are inward.  Is there any way to reverse normals for
the first extruded surface or any other ways to build an extrusion with the
outward normals?

The code for the cylinder is below:

// -- Parameters
---------------------------------------------------------------
    // left end section center point
cx = 0.0;
cy = 0.0;
cz = 0.0;

    // section radious
r = 0.3;

    // length
length = 1.0;

    // characteristic lenght (mesh density)
cl = 0.142;

// -- Points
-------------------------------------------------------------------
Point(1) = {cx, cy,     cz,     cl};
Point(2) = {cx, cy + r, cz,     cl};
Point(3) = {cx, cy - r, cz,     cl};
Point(4) = {cx, cy,     cz + r, cl};
Point(5) = {cx, cy,     cz - r, cl};

// -- Curves
-------------------------------------------------------------------
Circle(1) = {2, 1, 4};
Circle(2) = {4, 1, 3};
Circle(3) = {3, 1, 5};
Circle(4) = {5, 1, 2};

// -- Surfaces
-----------------------------------------------------------------
Line Loop(1) = {1, 2, 3, 4};
Plane Surface(1) = {1};

Extrude {cx + length, cy, cz} {
    Surface{1};
}

Sincerely,
Alexander
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