function E = EM1(n,i,k)
% EM1 elementary matrix of type I.
%
%   EM1(n,i,k) is an n-by-n matrix that permutes 
%   (interchanges) the i-th and k-th row any n-by-m 
%   matrix A (when multiplying A on the left). 
%
%   Matt Kawski 7-10-99
%   http://math.la.asu.edu/~kawski
%   kawski@asu.edu
%
E = eye(n);
   if ( i > n ) 
   disp('First index exceeds matrix dimension')
elseif ( i > n ) 
   disp('Second index exceeds matrix dimension')
else
   E(i,i) = 0;   
   E(i,k) = 1;   
   E(k,i) = 1;   
   E(k,k) = 0;
end