Abstract
For computational purposes such as debugging, derivative computations using the reverse mode of automatic differentiation, or optimal control by Newton’s method, one may need to reverse the execution of a program. The simplest option is to record a complete execution log and then to read it backwards. As a result, massive amounts of storage are normally required. This paper proposes a new approach to reversing program executions. The presented technique runs the forward simulation and the reversal process at the same speed. For that purpose, one only employs a fixed and usually small amount of memory pads called checkpoints to store intermediate states and a certain number of processors. The execution log is generated piecewise by restarting the evaluation repeatedly and concurrently from suitably placed checkpoints. The paper illustrates the principle structure of time-minimal parallel reversal schedules and quotes the required resources. Furthermore, some specific aspects of adjoint calculations are discussed. Initial results for the steering of a Formula 1 car are shown.
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