## Existence and uniqueness theorems for fourth-order boundary value problems.(English)Zbl 0634.34009

The differential equation (1) $$y^{(IV)}=f(x,y,y'')$$ is considered under the following types of boundary conditions:
(2) $$y(0)=y_ 0$$, $$y(1)=y_ 1$$, $$y''(0)=\bar y_ 0$$, $$y''(1)=\bar y_ 1$$;
(3) $$y(0)=y_ 0$$, $$y(1)=y_ 1$$, $$y''(0)=\bar y_ 0$$, $$y'''(1)=\bar y_ 1$$;
(4) $$y(0)=y(1)=y''(0)=y''(1)=0$$ or
(5) $$y(0)=y(1)=0$$; $$y'''(0)-hy''(0)=0$$, $$y'''(1)+ky''(1)=0$$, with $$h, k\geq 0$$, $$h+k>0$$.
Existence theorems for all of the boundary value problems (1-2)–(1-5) are obtained by application of Schauder’s fixed point theorem under continuity and boundedness hypotheses on $$f$$ and its partial derivative $$f_ 3$$. A uniqueness theorem is obtained for the problem (1-4) under the additional assumption of a bound on the partial derivative $$f_ 2$$. Further uniqueness results for the problem (1-2)–(1-5) are reduced to uniqueness questions for solutions of corresponding second order boundary value problems for the integrodifferential equation $u''=f(x,y_ 0+x(y_ 1- y_ 0)+\int^{1}_{0}G(x,t)u(t)\,dt,u)$ obtained by setting $$y''=u$$, with $$G(x,t)$$ the Green’s function for the problem $u''=0,\quad u(0)=u(1)=0.$ Boundary conditions of the form (2)–(5) have been less extensively studied than the familiar conjugate or focal-type problems. R. A. Usmani [Proc. Am. Math. Soc. 77, 329–335 (1979; Zbl 0424.34019)] has studied a problem of the form (1-2) in which the equation is linear and independent of $$y''$$.
Reviewer: L.J.Grimm

### MSC:

 34B15 Nonlinear boundary value problems for ordinary differential equations

Zbl 0424.34019
Full Text:

### References:

 [1] Bebernes, J.W.; Gaines, R., Dependence on boundary data and a generalized boundary-value problem, J. differential equations, 4, 359-368, (1968) · Zbl 0169.10602 [2] Corduneanu, C., Sopra I problemi ai limiti per alcuni sistemi di equazioni differenziali non lineari, Rend. acad. napoli, 4, 98-106, (1958) · Zbl 0091.26201 [3] Reiss, E.L.; Callegari, A.J.; Ahluwalia, D.S., Ordinary differential equations with applications, (1976), Holt, Rinehart & Winston Berlin/New York/Heidelberg · Zbl 0334.34002 [4] Usmani, R.A., A uniqueness theorem for a boundary value problem, (), 329-335, 3 · Zbl 0424.34019
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