%Calculate incidence matrix from adjacency matrix of a graph
%n = order, e = size of graph
%this file should be called incid.m, same as the function for this to work.
%usage: M=incid(n,A);
function M=incid(n,A)
e=0;
for i=1:n,
   for j=1:n,
      if A(i,j)==1 
         e=e+1;
         M(i,e)=1; %1st subscript is row label, ie vertex number
         M(j,e)=1; %second subscript is edge number
      end;
   end;
end;
%display(M);
%note that increasing e stepwise increases the size of the matrix M stepwise.
%this is inefficient for large e, there it would be better to estimate or calculate e
%beforehand.