Add executable to generate tensor network graphs

CMakeLists.txt

@@ -543,8 +543,13 @@ if (BUILD_TESTING)
       target_link_libraries(${example${i}} SeQuant)
     endforeach ()
 
+	set(example12 "tensor_network_graphs")
+    add_executable(${example12} EXCLUDE_FROM_ALL
+            examples/${example12}/${example12}.cpp)
+    target_link_libraries(${example12} SeQuant)
+
     # add tests for running examples
-    set(lastexample 11)
+    set(lastexample 12)
     foreach (i RANGE ${lastexample})
         if (TARGET ${example${i}})
             add_dependencies(examples-sequant ${example${i}})

examples/tensor_network_graphs/tensor_network_graphs.cpp

@@ -0,0 +1,64 @@
+#include <SeQuant/core/runtime.hpp>
+#include <SeQuant/core/bliss.hpp>
+#include <SeQuant/core/parse_expr.hpp>
+#include <SeQuant/core/tensor.hpp>
+#include <SeQuant/core/tensor_network.hpp>
+#include <SeQuant/domain/mbpt/convention.hpp>
+
+#include <string>
+#include <cassert>
+#include <codecvt>
+#include <locale>
+#include <iostream>
+#include <optional>
+
+	using namespace sequant;
+
+std::wstring from_utf8(std::string_view str) {
+	std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
+	return converter.from_bytes(std::string(str));
+}
+
+std::optional<TensorNetwork> to_network(const ExprPtr &expr) {
+	if (expr.is<Tensor>()) {
+		return TensorNetwork({expr});
+	} else if (expr.is<Product>()) {
+		for (const ExprPtr &factor : expr.as<Product>().factors()) {
+			if (!factor.is<Tensor>()) {
+				return {};
+			}
+		}
+
+		return TensorNetwork(expr.as<Product>().factors());
+	} else {
+		return {};
+	}
+}
+
+int main(int argc, char **argv) {
+
+	set_locale();
+	mbpt::set_default_convention();
+
+	for (std::size_t i = 1; i < static_cast<std::size_t>(argc); ++i) {
+		std::wstring current = from_utf8(argv[i]);
+		ExprPtr expr;
+		try {
+			expr = parse_expr(current);
+		} catch (const ParseError &e) {
+			std::wcout << "Failed to parse expression '" << current << "': " << e.what() << std::endl;
+			return 1;
+		}
+		assert(expr);
+
+		std::optional<TensorNetwork> network = to_network(expr);
+		if (!network.has_value()) {
+			std::wcout << "Failed to construct tensor network for input '" << current << "'" << std::endl;
+			return 2;
+		}
+
+		TensorNetwork::Graph graph = network->create_graph();
+		std::wcout << "Graph for '" << current << "'\n";
+		graph.bliss_graph->write_dot(std::wcout, graph.vertex_labels);
+	}
+}