public static void Serialize()

in Chemistry/src/DataModel/Serialization/LegacyFormats/FciDump.cs [111:158]
41 lines of code
3 McCabe index (conditional complexity)

        public static void Serialize(TextWriter writer, IEnumerable<ElectronicStructureProblem> problems)
        {
            var problem = problems.Single();

            // Start by writing the header.
            writer.WriteLine($"&FCI NORB={problem.NOrbitals},NELEC={problem.NElectrons},");
            // Assume global phase symmetry for now.
            writer.WriteLine($" ORBSYM={String.Join("", Enumerable.Range(0, problem.NOrbitals).Select(idx => "1,"))}");
            writer.WriteLine($" ISYM=1,");
            writer.WriteLine("&END");

            (string, double) FormatTerm(KeyValuePair<OrbitalIntegral, DoubleCoeff> term) =>
                (
                    String.Join(" ",
                        ConvertIndices(
                            term.Key.OrbitalIndices,
                            OrbitalIntegral.Convention.Dirac,
                            OrbitalIntegral.Convention.Mulliken
                        )
                        .ToOneBasedIndices()
                    ),
                    term.Value
                );

            foreach (var (indices, value) in problem
                                 .OrbitalIntegralHamiltonian
                                 .Terms[TermType.OrbitalIntegral.TwoBody]
                                 .Select(FormatTerm))
            {
                writer.WriteLine($"{value} {indices}");
            }
            // Next write out all one-body terms, using trailing zeros to indicate one-body.
            foreach (var (indices, value) in problem
                                 .OrbitalIntegralHamiltonian
                                 .Terms[TermType.OrbitalIntegral.OneBody]
                                 .Select(FormatTerm))
            {
                writer.WriteLine($"{value} {indices} 0 0");
            }
            // Finish by writing out the identity term.
            var identityTerm = problem
                .OrbitalIntegralHamiltonian
                .Terms.GetValueOrDefault(TermType.OrbitalIntegral.Identity, null)
                ?.Select(term => term.Value.Value)
                ?.SingleOrDefault() ?? 0.0
                + problem.EnergyOffset.Value;
            writer.WriteLine($"{identityTerm} 0 0 0 0");
        }