# Build mesh from a vector of nodes
**URL:** https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479
**Category:** General Discussion
**Created:** [February 7, 2022, 10:24pm UTC](https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479 "2022-02-07T22:24:43Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@larismartins](https://community.freefem.org/u/larismartins)
#### Post date: [February 7, 2022, 10:24pm UTC](https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479/1 "2022-02-07T22:24:43Z")
I’m trying to build a mesh using a vector of nodes
```auto
real[int,int] nodes = [[0,0],
[0.5,0],
[1,0],
[0,0.5],
[0.5,0.5],
[1,0.5],
[0,1],
[0.5,1],
[1,1]];
border bdry(t=0,nodes.n-1){ P.x=nodes(0,t); P.y=nodes(1,t); label=1; };
plot(bdry(nodes.n-1),dim=2,wait=1,cmm="boundary");
mesh Th = buildmesh(bdry(nodes.n-1),fixeborder=true);
plot(Th,wait=1,cmm="mesh");
```
But I get the following error:
```auto
Out of bound 0 <=0 < 9 2 < 2 array type = P3KNMIdE
current line = 11
```
What am I doing wrong?
---
### Author:  [@fivanci](https://community.freefem.org/u/fivanci)
#### Post date: [February 8, 2022, 2:06am UTC](https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479/2 "2022-02-08T02:06:16Z")
The way you set up your matrix of nodes, it is \in\mathbb{R}^{9\times2}. You are treating it somehow mixed, like sometimes as \in\mathbb{R}^{9\times2} an sometimes as \in\mathbb{R}^{2\times 9}. Check the documentation [Types](https://doc.freefem.org/references/types.html#matrix-size) for `matrix size`.
```auto
real[int,int] nodes = [[0,0],[0.5,0],[1,0],[0,0.5],[0.5,0.5],[1,0.5],[0,1],
[0.5,1],[1,1]];
// cout << nodes << endl;
cout << "nrows = " << nodes.n << ", ncols" << nodes.m << endl;
border bdry(t=0,nodes.n-1){ P.x=nodes(t,0); P.y=nodes(t,1); label=1; };
plot(bdry(nodes.n-1),dim=2,wait=1,cmm="boundary");
```
Also, your boundary is not a closed loop, so it won’t mesh of course.
Check also post [Building a border from an array of vertices - #2 by fivanci](https://community.freefem.org/t/building-a-border-from-an-array-of-vertices/1253/2), although, I see now there is _lapsus calami_ in there as well. It should be, in declaration,
`real[int,int] vtxCoords(2,nn);` and later in code `vtxCoords.n-1`\mapsto`vtxCoords.m-1`.
if
---
### Author:  [@larismartins](https://community.freefem.org/u/larismartins)
#### Post date: [February 8, 2022, 2:15pm UTC](https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479/3 "2022-02-08T14:15:39Z")
Do you know a way to build a mesh using connectivity matrix? Something like:
```auto
matrix elems = [[1,2,5,4],
[2,3,6,5],
[4,5,8,7],
[5,6,9,8]];
matrix edges = [[1,2],
[2,3],
[1,4],
[2,5],
[3,6],
[4,5],
[5,6],
[4,7],
[5,8],
[6,9],
[7,8],
[8,9]];
```
I’m trying to get control over all edges, boundary and internal. Also, I wouldlike to label each edge
---
### Author:  [@fivanci](https://community.freefem.org/u/fivanci)
#### Post date: [February 9, 2022, 1:51am UTC](https://community.freefem.org/t/build-mesh-from-a-vector-of-nodes/1479/4 "2022-02-09T01:51:48Z")
> [@larismartins](#):
>
> I’m trying to get control over all edges, boundary and internal. Also, I wouldlike to label each edge
When you say label, you mean label each edge in the triangle ( local [1,2,3] \mapsto global [i\_1,i\_2,i\_3] ) ? I.e., by
> [@larismartins](#):
>
> control over all edges
you mean (global) label each edge in the mesh by hand ?
1. In that case, **why use automatic mesh generator**? Seems to me it is easier to just write the mesh file directly – I am assuming you are checking some technical things and need only relatively small mesh (with small amount of entities), otherwise this would be a tedious procedure. If this is indeed the case, please read the documentation, e.g. [Mesh Generation](https://doc.freefem.org/documentation/mesh-generation.html#format-of-mesh-data) (there is everything you need). Also, for mesh connectivity you can check [Mesh Generation](https://doc.freefem.org/documentation/mesh-generation.html#mesh-connectivity-and-data) .
2. Alternatively, command `change(...)` ([Mesh Generation](https://doc.freefem.org/documentation/mesh-generation.html#the-command-change)) might also be of interest since it gives a certain amount of control over mesh entities. Actually, in the documentation it says you can prescribe a new numbering of both vertices and elements (`renumv`, `renumt`), although I never played with this.
3. As a third option, you might want to look at _gmsh_ software and explicitly construct your mesh via _.geo_ file – a tradeoff (up to some extent) between writing by hand directly a mesh into file and automatic mesh generation. You can have a great control over mesh entities labeling with a little bit of writing.
if