The Cost of Flattening with Common Subexpression Elimination
نویسندگان
چکیده
Compiling a solver-independent constraint model to solver input usually involves flattening, the decomposition of complex constraints into simpler expressions to suit the solver, introducing additional variables and constraints. In previous work [8], we have proposed extending flattening with common subexpression elimination (CSE) which can reduce the overhead introduced during flattening. In this work, we formally analyse the cost of standard flattening and CSEbased flattening: we compare time and space complexity and investigate the potential variable and constraint reduction from CSE-based flattening, its scope and limitations. Furthermore, we discuss flattening whole problem classes and show how to integrate CSE into class-wise flattening. We highlight the differences to instance-wise flattening and discuss open questions. Finally, our empirical analysis confirms our theoretical findings and demonstrates the benefits of CSE-based flattening.
منابع مشابه
Effective compilation of constraint models
Compiling solver-independent constraint models to solver input typically involves flattening, the decomposition of complex expressions into simpler expressions, introducing additional variables and constraints. In previous work [8], we have informally proposed extending flattening problem instances with common subexpression elimination(CSE), a widespread optimisation technique that has not yet ...
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