Function flatten_einsum

fem/tensorcoefficient.cpp:483–509

        }

        pair<string, Array<shared_ptr<CoefficientFunction>>>
        flatten_einsum(const string& signature,
                       const Array<shared_ptr<CoefficientFunction>>& cfs,
                       const map<string, bool> &options) {

          Array<shared_ptr<CoefficientFunction>> new_cfs;
          new_cfs.SetAllocSize(cfs.Size());

          cout << IM(5) << "EinsumCF: flatten einsum CF (no recursion)" << endl;
          auto parts = split_signature(signature);

          string used_symbols = signature;

          for (auto i : Range(cfs))
            if (auto cfi = dynamic_pointer_cast<EinsumCoefficientFunction>(cfs[i]); cfi)
              {
                auto nested_signature = cfi->ExpandedIndexSignature();
                parts[i] = expand_einsum_part(parts[i], nested_signature, used_symbols);
                used_symbols += parts[i];
                auto nested_inputs = cfi->ExpandedInputCoefficientFunctions();
                new_cfs.Append(nested_inputs);
              }
            else
              new_cfs.Append(cfs[i]);

          return {form_index_signature(parts), std::move(new_cfs)};
        }

        bool is_identity(const shared_ptr<CoefficientFunction> cf) {
          if (dynamic_pointer_cast<IdentityCoefficientFunction>(cf))