[drake_cmake_installed] Replace broken particles example (#355)

For now, just sync up with the drake_cmake_installed_apt example.
It is not a great demo, but it's what we have.

drake_cmake_installed/CMakeLists.txt

@@ -19,7 +19,7 @@ execute_process(COMMAND ${Python3_EXECUTABLE}-config --exec-prefix
 )
 list(APPEND CMAKE_PREFIX_PATH "${PYTHON_EXEC_PREFIX}")
 
-get_filename_component(PYTHONPATH
+get_filename_component(DRAKE_PYTHONPATH
   "${drake_DIR}/../../python${Python3_VERSION_MAJOR}.${Python3_VERSION_MINOR}/site-packages"
   REALPATH
 )

drake_cmake_installed/README.md

@@ -49,14 +49,6 @@ cd drake-external-examples
 mkdir drake_cmake_installed-build && cd drake_cmake_installed-build
 cmake -DCMAKE_PREFIX_PATH=$HOME/drake ../drake_cmake_installed
 make
-
-###############################################################
-# Execute
-###############################################################
-# A demo
-$HOME/drake/bin/drake-visualizer &
-(cd src/particles && exec ./uniformly_accelerated_particle)
-
 # (Optionally) Run Tests
 make test
 ```
@@ -66,7 +58,7 @@ make test
 Drake specific Examples:
 
 * [Simple Continuous Time System](src/simple_continuous_time_system/README.md)
-* [Particle Demo](src/particles/README.md)
+* [Particle System](src/particle)
 * [Find Resources](src/find_resource/README.md)
 
 # Developer Testing

drake_cmake_installed/setup/install_prereqs

@@ -50,9 +50,6 @@ case "$OSTYPE" in
     curl -o drake.tar.gz https://drake-packages.csail.mit.edu/drake/nightly/drake-latest-mac-arm64.tar.gz
     trap 'rm -f drake.tar.gz' EXIT
     tar -xf drake.tar.gz -C /opt
-
-    # Install additional dependencies needed to build example
-    brew bundle --file="$(dirname "${BASH_SOURCE}")/Brewfile"
     ;;
 
     linux*)
@@ -83,7 +80,6 @@ EOF
 
     apt-get update
     apt-get install --no-install-recommends $(cat <<EOF
-      libgflags-dev
       python3-all-dev
 EOF
     )
@@ -93,4 +89,4 @@ esac
 # Show version for debugging; use echo for newline / readability.
 echo -e "\ndrake VERSION.TXT: $(cat /opt/drake/share/doc/drake/VERSION.TXT)\n"
 
-/opt/drake/share/drake/setup/install_prereqs
+/opt/drake/share/drake/setup/install_prereqs

drake_cmake_installed/src/CMakeLists.txt

@@ -1,13 +1,13 @@
 # SPDX-License-Identifier: MIT-0
 
 add_subdirectory(find_resource)
-add_subdirectory(particles)
+add_subdirectory(particle)
 add_subdirectory(simple_bindings)
 add_subdirectory(simple_continuous_time_system)
 
 add_test(NAME import_all_test COMMAND
   "${Python3_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/import_all_test.py"
 )
 set_tests_properties(import_all_test PROPERTIES
-  ENVIRONMENT "PYTHONPATH=${PYTHONPATH}"
+  ENVIRONMENT "PYTHONPATH=${DRAKE_PYTHONPATH}"
 )

drake_cmake_installed/src/find_resource/CMakeLists.txt

@@ -8,5 +8,5 @@ add_test(NAME find_resource_example_py COMMAND
   "${Python3_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/find_resource_example.py"
 )
 set_tests_properties(find_resource_example_py PROPERTIES
-  ENVIRONMENT "PYTHONPATH=${PYTHONPATH}"
+  ENVIRONMENT "PYTHONPATH=${DRAKE_PYTHONPATH}"
 )

drake_cmake_installed/src/particle/CMakeLists.txt

@@ -0,0 +1,20 @@
+# SPDX-License-Identifier: MIT-0
+
+add_library(particle particle.cc particle.h)
+target_link_libraries(particle drake::drake)
+
+add_executable(particle_test particle_test.cc)
+target_link_libraries(particle_test particle drake::drake gtest)
+add_test(NAME cc_particle_test COMMAND particle_test)
+set_tests_properties(cc_particle_test PROPERTIES LABELS small TIMEOUT 60)
+
+add_test(NAME python_particle_test
+  COMMAND Python3::Interpreter -B -m unittest particle_test
+)
+set_tests_properties(python_particle_test PROPERTIES
+  ENVIRONMENT "PYTHONPATH=${DRAKE_PYTHONPATH}"
+  LABELS small
+  REQUIRED_FILES "${CMAKE_CURRENT_SOURCE_DIR}/particle_test.py"
+  TIMEOUT 60
+  WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
+)

drake_cmake_installed/src/particles/particle.h → drake_cmake_installed/src/particle/particle.h

@@ -22,19 +22,14 @@ namespace particles {
 ///   - linear position (state/output index 0), in @f$ m @f$ units.
 ///   - linear velocity (state/output index 1), in @f$ m/s @f$ units.
 ///
-/// @tparam T must be a valid Eigen ScalarType.
-///
-/// @note
-/// Instantiated templates for the following scalar types
-/// @p T are provided:
-///
-/// - double
+/// @tparam_double_only
 ///
 template <typename T>
 class Particle final : public drake::systems::LeafSystem<T> {
  public:
   DRAKE_NO_COPY_NO_MOVE_NO_ASSIGN(Particle);
 
+  /// A constructor that initializes the system.
   Particle();
 
  protected:

drake_cmake_installed/src/particle/particle.py

@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: MIT-0
+
+from pydrake.systems.framework import BasicVector
+from pydrake.systems.framework import LeafSystem
+from pydrake.systems.framework import PortDataType
+
+
+class Particle(LeafSystem):
+    """
+    A linear 1DOF particle system.
+
+    With very simple dynamics xdotdot = a, this system can be described in
+    terms of its:
+
+    Inputs:
+        linear acceleration (input index 0), in m/s^2 units.
+
+    States/Outputs:
+        linear position (state/output index 0), in m units.
+        linear velocity (state/output index 1), in m/s units.
+    """
+    def __init__(self):
+        LeafSystem.__init__(self)
+        # A 1D input vector for acceleration.
+        self.DeclareInputPort('acceleration', PortDataType.kVectorValued, 1)
+        # Adding one generalized position and one generalized velocity.
+        self.DeclareContinuousState(1, 1, 0)
+        # A 2D output vector for position and velocity.
+        self.DeclareVectorOutputPort('postion_and_velocity', BasicVector(2),
+                                     self.CopyStateOut)
+
+    def CopyStateOut(self, context, output):
+        # Get current state from context.
+        continuous_state_vector = context.get_continuous_state_vector()
+        # Write system output.
+        output.SetFromVector(continuous_state_vector.CopyToVector())
+
+    def DoCalcTimeDerivatives(self, context, derivatives):
+        # Get current state from context.
+        continuous_state_vector = x = context.get_continuous_state_vector()
+        # Obtain the structure we need to write into.
+        derivatives_vector = derivatives.get_mutable_vector()
+        # Get current input acceleration value.
+        input_vector = self.EvalVectorInput(context, 0)
+        # Set the derivatives. The first one is velocity and the second one is
+        # acceleration.
+        derivatives_vector.SetAtIndex(0, continuous_state_vector.GetAtIndex(1))
+        derivatives_vector.SetAtIndex(1, input_vector.GetAtIndex(0))

drake_cmake_installed/src/particle/particle_test.py

@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: MIT-0
+
+import unittest
+
+from particle import Particle
+
+
+class TestParticle(unittest.TestCase):
+    """A test case for Particle systems."""
+    def setUp(self):
+        # System (aka 'device under test') being tested.
+        self.dut = Particle()
+        # Context for the given dut.
+        self.context = self.dut.CreateDefaultContext()
+        # Outputs of the given dut.
+        self.output = self.dut.AllocateOutput()
+        # Derivatives of the given dut.
+        self.derivatives = self.dut.AllocateTimeDerivatives()
+
+    def test_output(self):
+        """
+        Makes sure a Particle output is consistent with its state (position and
+        velocity).
+        """
+        # Initialize state.
+        continuous_state_vector = \
+            self.context.get_mutable_continuous_state_vector()
+        continuous_state_vector.SetAtIndex(0, 10.0)  # x0 = 10 m.
+        continuous_state_vector.SetAtIndex(1, 1.0)  # x1 = 1 m/s.
+        # Compute outputs.
+        self.dut.CalcOutput(self.context, self.output)
+        output_vector = self.output.get_vector_data(0)
+        # Check results.
+        self.assertEqual(output_vector.GetAtIndex(0), 10.0)  # y0 == x0
+        self.assertEqual(output_vector.GetAtIndex(1), 1.0)  # y1 == x1
+
+    def test_derivatives(self):
+        """
+        Makes sure a Particle system state derivatives are consistent with its
+        state and input (velocity and acceleration).
+        """
+        # Set input.
+        input_port = self.dut.get_input_port(0)
+        input_port.FixValue(self.context, 1.0)  # u0 = 1 m/s^2
+        # Set state.
+        continuous_state_vector = \
+            self.context.get_mutable_continuous_state_vector()
+        continuous_state_vector.SetAtIndex(0, 0.0)  # x0 = 0 m
+        continuous_state_vector.SetAtIndex(1, 2.0)  # x1 = 2 m/s
+        # Compute derivatives.
+        self.dut.CalcTimeDerivatives(self.context, self.derivatives)
+        derivatives_vector = self.derivatives.get_vector()
+        # Check results.
+        self.assertEqual(derivatives_vector.GetAtIndex(0), 2.0)  # x0dot == x1
+        self.assertEqual(derivatives_vector.GetAtIndex(1), 1.0)  # x1dot == u0
+
+
+if __name__ == '__main__':
+    unittest.main()