Edge orientation

General Discussion
1

Is it possible to find the edge orientation on a mesh?

mesh P = square(2,2);
int NbTriangles = P.nt; //number of triangles
plot(P, wait=1);

fespace LambdaH(P, P0edge);
fespace V0(P,P0);

V0 u0;
LambdaH l0;

int nDoFu0 = V0.ndof;
int nDoFl0 = LambdaH.ndof;

int nDoFu0K = V0.ndofK;
int nDoFl0K = LambdaH.ndofK;

V0 uX = x, uY = y;
LambdaH lX = x, lY = y;

real[int,int] CoordDoFl0(nDoFl0,2);

for(int i= 0; i< nDoFu0; i++)
 cout << uX[][i] << " " << uY[][i] << "\n";

for(int i= 0; i <nDoFl0; i++){
 CoordDoFl0(i,0) = lX[][i];
 CoordDoFl0(i,1) = lY[][i];
 cout << CoordDoFl0 << "\n";
 //cout << lX[][i] << " " << lY[][i] << "\n";
}

I’ve built a matrix with the coordinates of each DoF, now I would like to know the edge orientation.

2

Yes the edge orientation is given by the vertex number go form the lowest vertex number to the biggest vertex number.

Otherwise in intalledge integral the function edgeOrientation get +1 or -1 depending of the orientation.

3

One more question, for example, I defined the following space:

fespace LambdaH(P, P0edge);

and I have the DoF for each element

8 3	
	   6   9   5
	  12  10   9
	   0   2   1
	   4   6   2
	  11  13  12
	  14  15  13
	   3   7   4
	   8  11   7

I want to build a matrix with the edge orientation, something like:
for element 1: 1 1 -1

Is it possible?

4

I tried to use the function edgeOriention as shown in the manual, but it is not working. I know the nodes of each element, so for example:

element 1: nodes 0 1 4
the sign of edge from 0 to 1: +1
the sign of edge from 1 to 4: +1
the sign of edge from 4 to 1: -1

those are the values that I want to store in a vector (or matrix)

edgeOrientation

Sign of i−j if the current edge is [qi,qj].

real S = int1d(Th, 1)(edgeOrientation);

5

Yes the code :

mesh Th=square(4,4);
fespace LambdaH(Th, P0edge);
matrix orient(Th.nt,LambdaH.ndof);
for(int k=0;  k<Th.nt;++k)
  for( int i=0; i<3;++i)
   {
      int j = LambdaH(k,i); 
      int i1 = Th[k][(i+1)%3]; 
      int i2 = Th[k][(i+2)%3]; 
      orient(k,j) = i1 < i2 ? 1 : -1; 
     
}
cout << orient << endl;
6

I’m getting th following error

Error line number 3, in file C:\Users\LARISS~1\AppData\Local\Temp\.ffcs21024.edp, before  token )

  current line = 3
Compile error : 
	line number :3, )
error Compile error : 
	line number :3, )
 code = 1 mpirank: 0
FreeFem++ returned error 1
7

You FreeFem version is too old , cf:

tions/FreeFem++.app/Contents/ff-4.10/bin/ffglut’ ;exit;
– FreeFem++ v4.10 (Lun 14 fév 2022 22:27:04 CET - git v4.10-60-g89b58302)
file : bbbbb.edp
Load: lg_fem lg_mesh lg_mesh3 eigenvalue
1 : mesh Th=square(4,4);
2 : fespace LambdaH(Th, P0edge);
3 : matrix orient(Th.nt,LambdaH.ndof);
4 : for(int k=0; k<Th.nt;++k)
5 : for( int i=0; i<3;++i)
6 : {
7 : int j = LambdaH(k,i);
8 : int i1 = Th[k][(i+1)%3];
9 : int i2 = Th[k][(i+2)%3];
10 : orient(k,j) = i1 < i2 ? 1 : -1;
11 :
12 : }
13 : cout << orient << endl; sizestack + 1024 =1384 ( 360 )

– Square mesh : nb vertices =25 , nb triangles = 32 , nb boundary edges 16

HashMatrix Matrix (COO) 0x600000f74000

n m nnz half fortran state

32 56 96 0 0 0 0
0 36 1
0 30 -1
0 29 1

1 Like
8

I’m using FreeFem++ -cs 14.3

9

I need the FreeFeM++ version not the version of FreeFem+±cs.

Sorry I think the version is 3.xx for me (too old) except is Antoine do a new version

In the FAQ it say :

Yes, starting from FreeFEM-cs version 15, FreeFEM-cs and FreeFEM are kept in separate packages to allow everyone to pick the versions that they need.

so please use the version 4.10 !!!

1 Like