We study optimal control problems for partial differential equations (focusing on the multidimensional differential equation) with control functions in the Dirichlet boundary conditions under pointwise control (and we admit state - by assuming weak hypotheses) constraints.
                    
                 
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                    
                       
We discuss the solvability of a nonhomogeneous boundary value problem for the semilinear equation of the vibrating string  in a bounded domain and with a certain type of superlinear nonlinearity. To this end we derive a new dual variational method.
                    
                 
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                    
                       
In this paper we establish the existence of nontrivial solutions to 
with  superlinear in .
                    
                 
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                    
                       
The existence of positive solutions for a nonlocal boundary-value problem with vector-valued response is investigated. We develop duality and variational principles for this problem. Our variational approach enables us to approximate solutions and give a measure of a duality gap between the primal and dual functional for minimizing sequences.
                    
                 
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                
                    
                
            
        
        
        
            
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