De la Vallée-Poussin multiple-point problem
The problem of finding a solution to an ordinary non-linear differential equation of order ,
or to a linear equation
where , , , subject to the conditions
It was shown by Ch.J. de la Vallée-Poussin  that if , , and if the inequality
where , , , is met, there exists a unique solution of the problem (2), (3). He also showed that if is continuous in all its arguments and satisfies a Lipschitz condition with constant in the variable , , then, if equation (4) is satisfied, there can be only one solution of the problem (1), (3).
The following aspects of the de la Vallée-Poussin multiple point problem are studied: improvement of an estimate of the number by changing the coefficients of (4); extension of the class of functions , , or ; and generalization of the conditions (3). A main problem is to prove that the solution exists and that it is unique. As far as the problem (2), (3) is concerned, this is equivalent with the following statement: Any non-trivial solution of equation (2) has at most zeros on (non-oscillation of solutions or separation of zeros).
|||Ch.J. de la Vallée-Poussin, "Sur l'equation différentielle linéaire du second ordre. Détermination d'une intégrale par deux valeurs assignées. Extension aux équations d'ordre " J. Math. Pures Appl. , 8 (1929) pp. 125–144|
|||G. Sansone, "Equazioni differenziali nel campo reale" , 1 , Zanichelli (1948)|
This problem is also known as the multipoint boundary value problem; it is mostly of historical interest. In [a1] an extension of de la Vallée-Poussin's result is given.
|[a1]||P. Hartman, "Ordinary differential equations" , Birkhäuser (1982)|
De la Vallée-Poussin multiple-point problem. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=De_la_Vall%C3%A9e-Poussin_multiple-point_problem&oldid=23246