On termination of integer linear loops

Joël Ouaknine, João Sousa Pinto, and James Worrell

A fundamental problem in program verification concerns the termination of simple linear loops of the form:

x := u ; WHILE Bx ≥ c DO {x := Ax + a}

where x is a vector of variables, u, a, and c are integer vectors, and A and B are integer matrices. Assuming the matrix A is diagonalisable, we give a decision procedure for the problem of whether, for all initial integer vectors u, such a loop terminates. The correctness of our algorithm relies on sophisticated tools from algebraic and analytic number theory, Diophantine geometry, and real algebraic geometry.

To the best of our knowledge, this is the first substantial advance on a 10-year-old open problem of Tiwari and Braverman.

Proceedings of SODA 15, 2015. 13 pages.

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