function G = givensmat(x)
%
%  Givens' matrix according to p. 195
%
   if abs(x(2)) >= abs(x(1))
      t = x(1)/x(2);
      s = 1/sqrt(1+t^2); 
      c = s*t;
   else
      t = x(2)/x(1); 
      c = 1/sqrt(1+t^2);
      s = c*t;
   end;
   G = [c, s; -s, c];