function T = tilt(n,rc,v);
%TILT	Tilt matrix.
%	T = TILT(n,rc,v) returns a tilt T from the 
%	n by n identity matrix.
%
%	RC is a constant specifying the type of transformation
% 	to be performed on the identity matrix.
%	RC = 1 means that a row of the n by n identity
%	matrix will be added to or subtracted from another row.
%	RC = 2 means that a column of the n by n identity 
%	matrix will be added to or subtracted from another column.
%
%	V is a two-component vector containing the indices
% 	of the two rows or columns used in the transformation.
%	V(1) specifies the row or column to be added to or
%       subtracted from the row or column specified by V(2).
%	In either case, the result is kept in the row or 
%	column specified by V(2). A negative V(1) means that the 
%       column or row specified by abs(V(1)) is to be subtracted
%	from the column or row specified by V(2).
%
%	For example, T = tilt(4,1,[-3 2]) returns a tilt T in 
%	which the third row of the 4 by 4 identity matrix is 
%	subtracted from the second row.
%
%	Note: V(2) should be positive.
%
%       See also FASTTILT
      
%	For use with A Matlab Guide to Linear Algebra by Harold M. Edwards.
%	By Serge Tchikanda. Last revised 09/18/96.

T = eye(n);	% creating the n by n identity matrix

if rc == 1       % checking if row operation	
 		        % is to be perfomed. 
   r1 = v(1);
   r2 = v(2); 

  if r1 < 0	
     T(r2,:) = T(r2,:) - T(abs(r1),:);    
  else
     T(r2,:) = T(r2,:) + T(abs(r1),:); 
  end

elseif rc == 2  	 % checking if column operation	
		         % is to be performed.  
   c1 = v(1);  
   c2 = v(2);	

   if c1 < 0	
      T(:,c2) = T(:,c2) - T(:,abs(c1));   
   else	
      T(:,c2) = T(:,c2) + T(:,abs(c1)); 
   end

else
   
  error('Unrecognizable operation')

end