From eaaee2e3056daafd63cd79a97275de5b6da5d013 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Mon, 19 Dec 2022 20:44:18 +0100
Subject: [PATCH] refactor: `total_energy` example refactored for V2

---
 example/total_energy.cpp | 114 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 example/total_energy.cpp

diff --git a/example/total_energy.cpp b/example/total_energy.cpp
new file mode 100644
index 00000000..8fec060c
--- /dev/null
+++ b/example/total_energy.cpp
@@ -0,0 +1,114 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include <units/isq/mechanics.h>
+#include <units/math.h>
+#include <units/natural/natural.h>
+#include <units/quantity_io.h>
+#include <units/si/constants.h>
+#include <units/si/unit_symbols.h>
+#include <exception>
+#include <iostream>
+
+template<class T>
+  requires units::is_scalar<T>
+inline constexpr bool units::is_vector<T> = true;
+
+namespace {
+
+using namespace units;
+
+quantity_of<isq::mechanical_energy> auto total_energy(weak_quantity_of<isq::momentum> auto p,
+                                                      weak_quantity_of<isq::mass> auto m,
+                                                      weak_quantity_of<isq::speed> auto c)
+{
+  return quantity_cast<isq::mechanical_energy>(sqrt(pow<2>(p * c) + pow<2>(m * pow<2>(c))));
+}
+
+void si_example()
+{
+  using namespace units::si::unit_symbols;
+  constexpr auto GeV = si::giga<si::electronvolt>;
+
+  constexpr quantity_of<isq::speed> auto c = 1. * si::si2019::speed_of_light_in_vacuum;
+  const weak_quantity_of<isq::momentum> auto p1 = 4. * isq::mechanical_energy[GeV] / c;
+  const weak_quantity_of<isq::mass> auto m1 = 3. * isq::mechanical_energy[GeV] / pow<2>(c);
+  const auto E = total_energy(p1, m1, c);
+
+  std::cout << "\n*** SI units (c = " << c << " = " << c[si::metre / s] << ") ***\n";
+
+  std::cout << "\n[in `GeV` and `c`]\n"
+            << "p = " << p1 << "\n"
+            << "m = " << m1 << "\n"
+            << "E = " << E << "\n";
+
+  const auto p2 = p1[GeV / (si::metre / s)];
+  const auto m2 = m1[si::giga<si::electronvolt> / pow<2>(si::metre / s)];
+  const auto E2 = total_energy(p2, m2, c)[GeV];
+
+  std::cout << "\n[in `GeV`]\n"
+            << "p = " << p2 << "\n"
+            << "m = " << m2 << "\n"
+            << "E = " << E2 << "\n";
+
+  const auto p3 = p1[kg * si::metre / s];
+  const auto m3 = m1[kg];
+  const auto E3 = total_energy(p3, m3, c)[J];
+
+  std::cout << "\n[in SI units]\n"
+            << "p = " << p3 << "\n"
+            << "m = " << m3 << "\n"
+            << "E = " << E3 << "\n";
+
+  std::cout << "\n[converted from SI units back to GeV]\n"
+            << "E = " << quantity_cast<GeV>(E3) << "\n";
+}
+
+void natural_example()
+{
+  using namespace units::natural;
+  using namespace units::natural::unit_symbols;
+
+  constexpr quantity_of<isq::speed> auto c = 1. * speed_of_light_in_vacuum;
+  const quantity_of<isq::momentum> auto p = 4. * momentum[GeV];
+  const quantity_of<isq::mass> auto m = 3. * mass[GeV];
+  const auto E = total_energy(p, m, c);
+
+  std::cout << "\n*** Natural units (c = " << c << ") ***\n"
+            << "p = " << p << "\n"
+            << "m = " << m << "\n"
+            << "E = " << E << "\n";
+}
+
+}  // namespace
+
+int main()
+{
+  try {
+    si_example();
+    natural_example();
+  } catch (const std::exception& ex) {
+    std::cerr << "Unhandled std exception caught: " << ex.what() << '\n';
+  } catch (...) {
+    std::cerr << "Unhandled unknown exception caught\n";
+  }
+}