Find the rows have two same elements from a matrix

I have a matrix (each row represents a traingle and each element represents a vertex ID of that traingle), I want to find which two traingles have two same vertices. This question can be demonstrated by the following example, for a matrix like the following:

1 9 8

2 7 8

5 8 9

6 5 4

7 3 8

5 4 8

the output would be [1, 3], [2, 5], and [3, 6], which are the rows have two same elements.

[Image Analyst]

What does each row and each column represent? Are you having triangles in 3-D, like (x, y, z)?

This looks like a homework problem. If you have any questions ask your instructor or read the link below to get started:

How do I get help on homework questions on MATLAB Answers? - MATLAB Answers - MATLAB Central

Obviously we can't give you the full solution because you're not allowed to turn in our code as your own.

[Jiafeng Ye]

This is not a homework question but a research one.

Each row represents a trainlge (consists of three vertices).

[Torsten]

A research is no homework ? Then you don't work at home for your research ?

Answer 1

[Torsten]

A = [1 9 8
     2 7 8
     5 8 9
     6 5 4
     7 3 8
     5 4 8];
[I,J] = meshgrid(1:size(A,1),1:size(A,1));
[rows cols] = find(arrayfun(@(i,j)numel(intersect(A(i,:),A(j,:))),I,J)==2);
tuples = [rows(rows < cols),cols(rows < cols)]

tuples = 4×2

1 3 2 5 3 6 4 6

Answer 2

[Matt J]

Use edges to get a list of all the edges of the triangulation. Then loop over the list and use edgeAttachments.