function OUT = angle1(x,y)

% ANGLE1 computes the angle from the horizontal axis to the point y - x

% Written by T.E.SMITH, 1/30/99 

%INPUTS: x = [x1,x2]
%        y = [y1,y2]

% OUT = angle

if ( y(1) == x(1))
   
   if (y(2) >= x(2))
      
      OUT = pi/2 ;
      
   else
      
      OUT = - (3*pi)/2 ;
      
   end
   
else 
   
   if (y(2) - x(2) > 0 )
      
      if (y(1) - x(1) > 0)
         
         OUT = atan((y(2) - x(2))/(y(1) - x(1))) ;
         
      else
         
         OUT = pi + atan((y(2) - x(2))/(y(1) - x(1))) ;
         
      end
      
   else 
      
      if (y(1) - x(1) > 0)
         
         OUT = 2*pi + atan((y(2) - x(2))/(y(1) - x(1))) ;
         
      else
         
         OUT = pi + atan((y(2) - x(2))/(y(1) - x(1))) ;
         
      end
      
   end
   
end