Method DiffJacobi

fem/tensorcoefficient.cpp:1399–1450

        }

        shared_ptr<CoefficientFunction>
        EinsumCoefficientFunction::DiffJacobi(
           const CoefficientFunction *var, T_DJC & cache) const
        {
          if (this == var)
            return IdentityCF(Dimensions());

          Array<int> res_dims;
          res_dims.Append(Dimensions());
          res_dims.Append(var->Dimensions());

          auto dres = ZeroCF(res_dims);
          try
          {
              // IMPORTANT NOTE:
              // use "original_index_signature" and "original_inputs" as only
              // these protect variables etc, i.e. they do not carry any
              // optimization!
              auto parts = split_signature(original_index_signature);

              for (size_t i: Range(original_inputs.Size()))
              {
                auto new_inputs{original_inputs};
                new_inputs[i] = original_inputs[i]->DiffJacobi(var,cache);
                if (new_inputs[i]->IsZeroCF())
                  continue;
                auto new_parts{parts};
                new_parts[i] = parts[i] + "...";
                new_parts.back() += "...";
                dres = dres + EinsumCF(form_index_signature(new_parts), new_inputs, options);
              }

              // TODO: great potential for optimization when equivalent objects are
              //  identified in Compile
              return dres;
          }
          catch (const OutOfIndices& e)
          {
            if (options.find("optimize_path") == options.end() || !options.at("optimize_path"))
            {
              cout << "Caught exception during DiffJacobi:\n"
                   << e.What()
                   << "\n"
                   << "Trying again with a broken-down EinsumCF." << endl;
              auto opts = options;
              opts["optimize_path"] = true;
              opts["expand_einsum"] = false;
              return Optimize(opts)->DiffJacobi(var, cache);
            }
            throw e;
          }
        }

        shared_ptr<EinsumCoefficientFunction>
        EinsumCoefficientFunction::Optimize(const map<string, bool> &aoptions) const