[wideli]

I am completely new to the finite element/ finite volume modeling. I have some problems to understand the 'tags' of the .msh file. Hope someone can help me understand it.

I use Gmsh to define the domain for computation and to generate unstructured mesh. I further partition the mesh into several subdomains using the embedded functionality (Metis). Shown in the bottom is the complete .msh file, where the mesh is divided into 5 partitions.

Could someone explain me each of the tag associated with the element? For example, the output info of the 68th, 70th and 71st element is:

68 4 7 0 16 4 5 -2 -3 -4 12 11 1 7
70 4 8 0 16 5 4 -1 -2 -3 -5 13 8 12 1
71 4 8 0 16 5 5 -1 -2 -3 -4 13 12 11 1

The 1st integer of each row, 68/70/71, is the ordering of the element.
The 2nd integer, 4, is the element type, where the integer, 4, stands for the tetrahedron type.

The last 4 integers are the list of the vertex of each element, e.g., 12-11-1-7, 13-8-12-1 and 13-12-11-1 for the 68th, 70th and 71st element, respectively.

I do NOT understand the rest of the tags. The Gmsh manual does clarify these.

1. What do the 3rd to the 5th integers stand for, e.g., 7-0-16, 8-0-16 and 8-0-16 for the 68th, 70th and 71st element? And why, for the same type of element, the 1st integer of the lists, 7-0-16, 8-0-16 and 8-0-16, is different for different element?

2. The rest of tags, 4-5-(-2)-(-3)-(-4), 5-4-(-1)-(-2)-(-3)-(-5) and 5-5-(-1)-(-2)-(-3)-(-4), seem to be the information of partitioning. What does the 1st integer of the lists shown above stand for? And why, for different element, this number could be different? The 2nd one seems to be the partition-number. The negative integers are the ghost points, which is shared with the other elements belonging to different partitions.

Hope someone can guide me through it. Many many thanks in advance!

Juan


$MeshFormat
2.2 0 8
$EndMeshFormat
$Nodes
13
1 0 0 0
2 1 0 0
3 0 1 0
4 0 0 1
5 0.4999999999983151 0.5000000000016849 0
6 0.5000000000016849 0 0.4999999999983151
7 0 0 0.5000000000020587
8 0.4999999999986943 0 0
9 0 0.4999999999986943 0
10 0 0.5000000000016849 0.4999999999983151
11 0 0.2500000000000948 0.2500000000000934
12 0.2500000000000948 0 0.2500000000000934
13 0.2499999999992523 0.2500000000000948 0
$EndNodes
$Elements
71
1 15 2 0 -2 6
2 15 2 0 -1 13
3 15 2 0 1 1
4 15 2 0 2 2
5 15 2 0 3 3
6 15 2 0 4 4
7 1 2 0 -4 11 13
8 1 2 0 -3 10 13
9 1 2 0 -2 13 6
10 1 2 0 -1 6 11
11 1 2 0 1 3 5
12 1 2 0 1 5 2
13 1 2 0 2 2 6
14 1 2 0 2 6 4
15 1 2 0 3 4 7
16 1 2 0 3 7 1
17 1 2 0 4 1 8
18 1 2 0 4 8 2
19 1 2 0 5 1 9
20 1 2 0 5 9 3
21 1 2 0 6 3 10
22 1 2 0 6 10 4
23 2 2 0 -8 10 13 11
24 2 2 0 -7 13 11 9
25 2 2 0 -6 6 13 11
26 2 2 0 -5 10 6 13
27 2 2 0 -4 8 13 6
28 2 2 0 -3 6 11 7
29 2 2 0 -2 13 10 5
30 2 2 0 -1 1 13 11
31 2 2 0 -1 13 5 6
32 2 2 0 -1 6 11 7
33 2 2 0 -1 6 13 11
34 2 4 0 8 1 5 7 1 11
35 2 4 0 8 1 5 11 1 9
36 2 4 0 8 1 2 10 9 3
37 2 4 0 8 1 3 4 7 10
38 2 4 0 8 1 3 10 7 11
39 2 4 0 8 1 2 11 9 10
40 2 4 0 10 1 5 1 12 7
41 2 4 0 10 1 4 1 8 12
42 2 4 0 10 1 1 2 6 8
43 2 4 0 10 1 3 6 4 7
44 2 4 0 10 1 5 6 7 12
45 2 4 0 10 1 4 6 12 8
46 2 4 0 12 1 4 13 8 1
47 2 4 0 12 1 5 9 13 1
48 2 4 0 12 1 1 2 8 5
49 2 4 0 12 1 2 5 9 3
50 2 4 0 12 1 1 8 13 5
51 2 4 0 12 1 2 13 9 5
52 2 4 0 14 1 1 2 6 5
53 2 4 0 14 1 2 5 10 3
54 2 4 0 14 1 3 6 4 10
55 2 4 0 14 1 1 6 10 5
56 4 8 0 16 5 4 -1 -2 -3 -5 6 11 13 12
57 4 8 0 16 5 3 -1 -2 -4 -5 10 13 6 11
58 4 8 0 16 5 5 -1 -3 -4 -2 12 11 7 6
59 4 8 0 16 5 4 -1 -2 -3 -5 8 13 12 6
60 4 8 0 16 5 2 -1 -3 -4 -5 13 9 11 10
61 4 8 0 16 5 1 -2 -3 -4 -5 13 10 6 5
62 4 8 0 16 5 3 -1 -2 -4 -5 7 10 4 6
63 4 8 0 16 5 1 -2 -3 -4 -5 5 8 2 6
64 4 7 0 16 4 2 -1 -3 -5 9 3 10 5
65 4 8 0 16 5 3 -1 -2 -4 -5 11 10 7 6
66 4 8 0 16 5 1 -2 -3 -4 -5 13 8 5 6
67 4 8 0 16 5 2 -1 -3 -4 -5 13 9 10 5
68 4 7 0 16 4 5 -2 -3 -4 12 11 1 7
69 4 8 0 16 5 5 -1 -2 -3 -4 9 13 11 1
70 4 8 0 16 5 4 -1 -2 -3 -5 13 8 12 1
71 4 8 0 16 5 5 -1 -2 -3 -4 13 12 11 1
$EndElements