On nonnegative solutions of SDDEs with an application to CARMA processes        
        
    
        Volume 8, Issue 3 (2021), pp. 309–328
            
    
                    Pub. online: 31 March 2021
                    
        Type: Research Article
            
                
             Open Access
Open Access
        
            
    
                Received
16 October 2020
                                    16 October 2020
                Revised
12 March 2021
                                    12 March 2021
                Accepted
12 March 2021
                                    12 March 2021
                Published
31 March 2021
                    31 March 2021
Abstract
This note provides a simple sufficient condition ensuring that solutions of stochastic delay differential equations (SDDEs) driven by subordinators are nonnegative. While, to the best of our knowledge, no simple nonnegativity conditions are available in the context of SDDEs, we compare our result to the literature within the subclass of invertible continuous-time ARMA (CARMA) processes. In particular, we analyze why our condition cannot be necessary for CARMA($p,q$) processes when $p=2$, and we show that there are various situations where our condition applies while existing results do not as soon as $p\ge 3$. Finally, we extend the result to a multidimensional setting.
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