qiskit.circuit.library.PhaseOracle.from_dimacs_file

classmethod PhaseOracle.from_dimacs_file(filename)

Create a PhaseOracle from the string in the DIMACS format.

It is possible to build a PhaseOracle from a file in DIMACS CNF format, which is the standard format for specifying SATisfiability (SAT) problem instances in Conjunctive Normal Form (CNF), which is a conjunction of one or more clauses, where a clause is a disjunction of one or more literals.

The following is an example of a CNF expressed in the DIMACS format:

c DIMACS CNF file with 3 satisfying assignments: 1 -2 3, -1 -2 -3, 1 2 -3.
p cnf 3 5
-1 -2 -3 0
1 -2 3 0
1 2 -3 0
1 -2 -3 0
-1 2 3 0

The first line, following the c character, is a comment. The second line specifies that the CNF is over three boolean variables — let us call them \(x_1, x_2, x_3\), and contains five clauses. The five clauses, listed afterwards, are implicitly joined by the logical AND operator, \(\land\), while the variables in each clause, represented by their indices, are implicitly disjoined by the logical OR operator, \(lor\). The \(-\) symbol preceding a boolean variable index corresponds to the logical NOT operator, \(lnot\). Character 0 (zero) marks the end of each clause. Essentially, the code above corresponds to the following CNF:

\((\lnot x_1 \lor \lnot x_2 \lor \lnot x_3) \land (x_1 \lor \lnot x_2 \lor x_3) \land (x_1 \lor x_2 \lor \lnot x_3) \land (x_1 \lor \lnot x_2 \lor \lnot x_3) \land (\lnot x_1 \lor x_2 \lor x_3)\).

Parameters

filename (str) – A file in DIMACS format.

Returns

A quantum circuit with a phase oracle.

Return type

PhaseOracle