Gelfand, I M <br/><br/>
Calculus of variations 

 - New York  Dover  1991 
 - xxiii, 813p.  
<br/><br/> Includes bibliographical references and index. 
<br/><br/><label>ISBN: </label>9780486414485 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Calculus -- Variations<br/>Euler equations -- Canonical form<br/>Mathematics<br/>Variational problems