[Gmsh] Using gmsh as library by C++, received warning message "Staring subloop x in Line Loop 1 (are you sure about this?)

[Guowei He]

Dear gmsh users and ,

When the following C++ code is executed to generate a simple rectangle with
a circular hole in it, based on the sample given by

Takuya OSHIMA, Ph.D. in http://www.geuz.org/pipermail/gmsh/2011/006803.html

, warning message "Staring subloop x in Line Loop 1 (are you sure about
this?) is prompted during the command "gmsh test.geo", though the geo graph
looks fine, the test.geo generated contains some thing like Line Loop(1) =
{1, 2, 3, 4, -6, -5}; where 1 2 3 4 are external boundaries and 5 6 are
edges of the circle. However a nicer approach in gmsh scripting is do
something like

// exterior boundary
ll1 = newll; Line Loop(ll1) = { l01, l02, l03, l04 };

// interstitial domain
s1 = news;   Plane Surface(s1) = { ll1, beadSurfLoops[] };

Is there some corresponding "Loops" object in gmsh library or we only use
something like "typedef   std::vector<GEdge *> Lineloop;
typedef std::vector<Lineloop> Loops;"?

Many thanks!

///////////////////////////////////////////////////////////////////
test.geo
////////////////////////////////////////////////////////////////////////////////
cl1 = 0.08;
Point(1) = {9.9, 8, 0, cl1};
Point(2) = {-9.9, 8, 0, cl1};
Point(3) = {-9.9, -8, 0, cl1};
Point(4) = {9.9, -8, 0, cl1};
Point(5) = {5, 5, 0, cl1};
Point(6) = {5, 7.5, 0, cl1};
Point(7) = {5, 2.5, 0, cl1};
Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 1};
Circle(5) = {6, 5, 7};
Circle(6) = {7, 5, 6};
Line Loop(1) = {1, 2, 3, 4, -6, -5};
Plane Surface(1) = {1};
Line Loop(2) = {5, 6};
Plane Surface(2) = {2};
Physical Line("inlet") = {1};
Physical Line("outlet") = {3};
Physical Line("wall") = {2, 4};
Physical Surface("interstitial") = {1};
Physical Surface("beadface") = {2};



//////////////////////////////////////////////////////////    rec.cpp
//////////////////////////////////////////////////////////////////////////////////
 // A simple Gmsh API demonstration program.
#include "Gmsh.h"
#include "GModel.h"
#include "MElement.h"
#include "MVertex.h"
#include <iostream>

typedef   std::vector<GEdge *> Lineloop;
typedef std::vector<Lineloop> Loops;

void *addBead(GModel *m, Loops &l, double const &cx, double const &cy,
double const &radius, double const &lc_bead) {
  Lineloop b;
  GVertex *gvc1c = m->addVertex(cx, cy, 0, lc_bead);
  GVertex *gvc1s = m->addVertex(cx, cy - radius, 0, lc_bead);
  GVertex *gvc1e = m->addVertex(cx, cy + radius, 0, lc_bead);
  GEdge *gec11 = m->addCircleArcCenter(gvc1s, gvc1c, gvc1e);
  GEdge *gec12 = m->addCircleArcCenter(gvc1e, gvc1c, gvc1s);

  b.push_back(gec11);
  b.push_back(gec12);
  l.push_back(b);
}

int main(int argc, char **argv)
{
  // Initialization.
  GmshInitialize(argc, argv);
  // Options may be set this way.
  // Output information messages generated by the Gmsh library.
  GmshSetOption("General", "Terminal", 1.);
  // Be verbose (output debug messages).
  GmshSetOption("General", "Verbosity", 99.);
  // Create GModel (the Gmsh library core) instance.
  GModel *m = new GModel;
  // Choices are "Gmsh" and "OCC" if the Gmsh library is compiled with
  // OpenCASCADE. Usually you want to use the "Gmsh" factory.
  m->setFactory("Gmsh");

  // Add vertices. Equivalent .geo directives are
  // cl1 = 0.1;
  // Point(1) = {-1, -1, 0, cl1};
  // Point(2) = {1, -1, 0, cl1};
  // Point(3) = {1, 1, 0, cl1};
  // Point(4) = {-1, 1, 0, cl1};
  // Point(5) = {0, 0, 0, cl1};
  const double lc_wall = 0.08, lc_bead = 0.08;

  // generating walls
  const double xmin = 10, xmax = -10, ymin = 10, ymax = -10, dx = 0.1, dy =
2;

  // corner points of rect domain
  GVertex *gv1 = m->addVertex(xmin - dx, ymin - dy, 0, lc_wall);
  GVertex *gv2 = m->addVertex(xmax + dx, ymin - dy, 0, lc_wall);
  GVertex *gv3 = m->addVertex(xmax + dx, ymax + dy, 0, lc_wall);
  GVertex *gv4 = m->addVertex(xmin - dx, ymax + dy, 0, lc_wall);

  // lines around the rect domain
  GEdge *ge1 = m->addLine(gv1, gv2);
  GEdge *ge2 = m->addLine(gv2, gv3);
  GEdge *ge3 = m->addLine(gv3, gv4);
  GEdge *ge4 = m->addLine(gv4, gv1);

  // // draw circle

  Loops ls;

  // exterior boundary
  Lineloop tmp;

  tmp.push_back(ge1);
  tmp.push_back(ge2);
  tmp.push_back(ge3);
  tmp.push_back(ge4);
  ls.push_back(tmp);

  // call the bead func
  int nBeads = 1;
  double radius = ymax / nBeads / 4;
  double cx = xmin / 2, cy = ymin / 2;
  for (int i = 0; i < nBeads; i++) {
    addBead(m, ls, cx, cy, radius, lc_bead);
    cx += 3 * radius;
  }


  // interstitial domain
  GFace *gf1 = m->addPlanarFace(ls);

  // create faces of beads
  Loops::iterator it = ls.begin();
  it++;
  std::vector<GRegion *> fbeads;
  Loops lst;
  int pn_beadface = m->setPhysicalName(nf_bead, dim_face);
  for (;it != ls.end(); it++) {
    lst.push_back(*it);
    GFace *gft = m->addPlanarFace(lst);
    gft->addPhysicalEntity(pn_beadface);
    lst.pop_back();
  }

  // The geometry constructed by the operations above may be saved this way.
  m->writeGEO("test.geo");

  // Create surface (2-D) mesh. Pass 3 to mesh() if creating a volume
  // (3-D) mesh.
  m->mesh(2);

  // // The created mesh may be saved this way.
  m->writeMSH("test.msh");



  // Finalization.
  delete m;
  GmshFinalize();
}


-- 
Kind regards,
Guowei He
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