Re-indexing matrix which corresponds to mesh

Hello

I'm wondering if anyone can help me. I'm trying to re-index two matrixes. I have selected a sub-sample of data and I need them to be re-numbered to 1:N. There is a corresponding matrix which is an Mx3 matrix which makes up the triangles.

I need to re-number the first matrax and then apply that re-numbered matrix to the list of triangles. This cannot be done by simple indexing because the numbers in the original matrix are obviously changed so they do not correspond with values in the 2nd matrix.

I'm not sure if I've explained that well but here is an example of the matrices I currently have.

I would also like to point out that those are just a sample number, the nodes may not necessarily match up below but they do in my matrices.

Cheers :)

Nodes:
3772
3947
3948
3949
4144
4145
4146
4147
4148
4149

Tri:
3771  3772  3603
3604  3603  3772
3773  3604  3772
3771  3946  3947
3948  3771  3947
3771  3948  3772
3772  3948  3949
3772  3949  3950
3772  3950  3773
3947  3946  4143

[Stephen23]

@Meghan Rochford: what do you expect the output based on those two sample matrices to be?

[KSSV]

The numbers shown in nodes and Tri are different..If they were same, we could attempt re-indexing..Check the given numbers once..are they correct?

[Meghan Rochford]

Yes in the larger matrix they are all the same. I want my nodes to be a list of 1:N (there are about 30 nodes in the original matrix). Then I want the corresponding number, assocaited with the nodes, in the triangle matrix.

Eaxmple:

Nodes:
1
2
3
4
5

Tri:
1,2,3
2,3,4
... etc

My issue is that the triangle matrix is not in order and I need to make sure I maintain the correct node ID. Does that make sense? I just can't wrap my head around indexing it correctly. I've never been too good at indexing!

[KSSV]

I got it..you are plotting unstructured mesh, you have extracted a part of it..and want to label them from 1:N...you can plot the subset...without changing indexing..

[Meghan Rochford]

That's I was doing originally but I have to manipulate the grid for that area and I need the nodes to start from 1. It was a requirement from my supervisors, I would rather keep it the way it is. But I have to do what they want!

[KSSV]

What you gave is the exact subset?

[Meghan Rochford]

The exact subset is:

Node=
3772
3947
3948
3949
4144
4145
4146
4147
4148
4149
4334
4335
4336
4337
4338
4339
4501
4502
4503
4504
4505
4506
4507
4690
3771
3604
3773
3771
3771
3950
4143
4333
4500
4500
4688
4689
4689
4689
3603
3604
3946
3771
3950
3946
4150
4333
4499
4500
4688
4689
4876
3603
3950
3773
4143
4143
4150
4333
4499

Triangles= 
3771  3772  3603
  3604  3603  3772
  3773  3604  3772
  3771  3946  3947
  3948  3771  3947
  3771  3948  3772
  3772  3948  3949
  3772  3949  3950
  3772  3950  3773
  3947  3946  4143
  4144  3947  4143
  3947  4144  4145
  4145  4146  3947
  3948  3947  4146
  4146  4147  3948
  3949  3948  4147
  4147  4148  3949
  3949  4148  4149
  4149  4150  3949
  3950  3949  4150
  4143  4333  4144
  4334  4144  4333
  4334  4335  4144
  4335  4145  4144
  4335  4336  4145
  4337  4145  4336
  4337  4146  4145
  4337  4338  4146
  4147  4146  4338
  4338  4339  4147
  4148  4147  4339
  4333  4499  4334
  4500  4334  4499
  4334  4500  4501
  4334  4501  4335
  4335  4501  4502
  4502  4336  4335
  4336  4502  4503
  4503  4504  4336
  4504  4505  4336
  4337  4336  4505
  4506  4337  4505
  4506  4338  4337
  4506  4507  4338
  4507  4339  4338
  4500  4688  4501
  4688  4689  4501
  4689  4502  4501
  4689  4690  4502
  4690  4503  4502
  4689  4876  4690

Answer 1

[KSSV]

Let nodes and tri be your Nodes and Triangles.

[val,idx] = unique(nodes) ;
nodes_1 = nodes ;
tri_1 = tri ;

for i = 1:length(val)
    nodes_1(nodes==val(i))=i ;
    tri_1(tri==val(i)) = i ;
end

tri_1 and nodes_1 are the Nodes and Triangles re-indexed to 1:N.

[Meghan Rochford]

You are a star! Thank you :)

Answer 2

[Andrei Bobrov]

Node_out = (1:numel(Node))';
[~,Triangles_out] = ismember(Triangles,Node);

or

[v,~,Node_out] = unique(Node,'stable');
Triangles_out = ismember(Triangles,v);

[Meghan Rochford]

I don't need to know if they belong to the same matrix. I know they do. I want to re-number the nodes and then correspondingly re-number the node ID in the triangle mesh.

[Sterling Baird]

Triangles_out is your new, renumbered triangulation. This is great, thank you! Neat application of ismember()