2,042 research outputs found
Cause Clue Clauses: Error Localization using Maximum Satisfiability
Much effort is spent everyday by programmers in trying to reduce long,
failing execution traces to the cause of the error. We present a new algorithm
for error cause localization based on a reduction to the maximal satisfiability
problem (MAX-SAT), which asks what is the maximum number of clauses of a
Boolean formula that can be simultaneously satisfied by an assignment. At an
intuitive level, our algorithm takes as input a program and a failing test, and
comprises the following three steps. First, using symbolic execution, we encode
a trace of a program as a Boolean trace formula which is satisfiable iff the
trace is feasible. Second, for a failing program execution (e.g., one that
violates an assertion or a post-condition), we construct an unsatisfiable
formula by taking the trace formula and additionally asserting that the input
is the failing test and that the assertion condition does hold at the end.
Third, using MAX-SAT, we find a maximal set of clauses in this formula that can
be satisfied together, and output the complement set as a potential cause of
the error. We have implemented our algorithm in a tool called bug-assist for C
programs. We demonstrate the surprising effectiveness of the tool on a set of
benchmark examples with injected faults, and show that in most cases,
bug-assist can quickly and precisely isolate the exact few lines of code whose
change eliminates the error. We also demonstrate how our algorithm can be
modified to automatically suggest fixes for common classes of errors such as
off-by-one.Comment: The pre-alpha version of the tool can be downloaded from
http://bugassist.mpi-sws.or
Proton-proton fusion in lattice effective field theory
The proton-proton fusion rate is calculated at low energy in a lattice
effective field theory (EFT) formulation. The strong and the Coulomb
interactions are treated non-perturbatively at leading order in the EFT. The
lattice results are shown to accurately describe the low energy cross section
within the validity of the theory at energies relevant to solar physics. In
prior work in the literature, Coulomb effects were generally not included in
non-perturbative lattice calculations. Work presented here is of general
interest in nuclear lattice EFT calculations that involve Coulomb effects at
low energy. It complements recent developments of the adiabatic projection
method for lattice calculations of nuclear reactions.Comment: 11 pages, 2 figure
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