s multiply 
          these vectors by m, since for any linear 
          transformation T, 
           
                T ( point  +  t1 * span1     +  t2 * span2 ) 
      
             =  T (point)  +  t1 * T(span1)  +  t2 * T(span2), 
            
          which means that T(point), T(span1), and T(span2) 
          are a point and spanning vectors for the transformed 
          plane. 
          ./
      
          <a href="mxv_c.html">mxv_c</a> ( m, point, tpoint ); 
          <a href="mxv_c.html">mxv