[matrix,I]=deleterepeatedrows(matrix)

function [matrix,I]=deleterepeatedrows(matrix)
%function: [element2edges, edge2nodes]=edge_numbering(elements)
%requires: deleterepeatedrows
%generates edges of (triangular) triangulation defined in elements
%elements is matrix, whose rows contain numbers of its element nodes 
%element2edges returns edges numbers of each triangular element
%edge2nodes returns two node numbers of each edge
%example: [element2edges, edge2nodes]=edge_numbering([1 2 3; 2 4 3])

[matrixs,tags] = sortrows(sort(matrix,2));

% which ones were reps?
k = find(all(diff(matrixs)==0,2));

%these rows of matrix are repeated 
repeated=tags(k);

%and these rows will be removed
removed=tags(k+1);

%both lists are sorted 
[removeds, tags2]=sort(removed);
repeateds=repeated(tags2);

% delete the tags to removed rows
tags(k+1) = [];
% and recover the original array, in the original order.
matrix = matrix(sort(tags),:);

%row indices before matrix compression indicating repetition   
I=insertvector((1:size(matrix,1))',repeateds,removeds);

%-------------------------------------------------------------
function r=insertvector(v,pos_from,pos_to)
     tf=false(1,numel(v)+numel(pos_to));
     r=double(tf);
     tf(pos_to)=true;
     r(~tf)=v;
     r(tf)=r(pos_from);    
%-------------------------------------------------------------