From 0b62d0104adbbd861559bf2c85a313e9229380ba Mon Sep 17 00:00:00 2001
From: Torsten Sommer <torsten.sommer@3ds.com>
Date: Tue, 27 Feb 2018 16:10:13 +0100
Subject: [PATCH] Add getDirectionalDerivative()

---
 docs/changelog.md                        |  6 +++
 fmpy/fmi2.py                             | 27 ++++++++++
 tests/test_get_directional_derivative.py | 63 ++++++++++++++++++++++++
 3 files changed, 96 insertions(+)
 create mode 100644 tests/test_get_directional_derivative.py

diff --git a/docs/changelog.md b/docs/changelog.md
index f3ad7cdd..b3bb8deb 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -1,3 +1,8 @@
+## v0.2.4 (unreleased)
+
+- `NEW` getDirectionalDerivative()
+
+
 ## v0.2.3 (2018-04-11)
 
 - `NEW` Allow simulation of extracted FMUs and pre-loaded model descriptions
@@ -16,6 +21,7 @@
 - `FIXED` Handling of time events
 - `FIXED` Conversion of Boolean start values
 
+
 ## v0.2.2 (2018-03-13)
 
 - `NEW` FMI 2.0 state serialization functions added
diff --git a/fmpy/fmi2.py b/fmpy/fmi2.py
index 1bdaeb56..332781f3 100644
--- a/fmpy/fmi2.py
+++ b/fmpy/fmi2.py
@@ -174,6 +174,12 @@ def __init__(self, **kwargs):
                            [fmi2Component, POINTER(fmi2Byte), c_size_t, POINTER(fmi2FMUstate)],
                            fmi2Status)
 
+        # Getting partial derivatives
+        self._fmi2Function('fmi2GetDirectionalDerivative',
+                           ['component', 'vUnknown_ref', 'nUnknown', 'vKnown_ref', 'nKnown', 'dvKnown', 'dvUnknown'],
+                           [fmi2Component, POINTER(fmi2ValueReference), c_size_t, POINTER(fmi2ValueReference), c_size_t, POINTER(fmi2Real), POINTER(fmi2Real)],
+                           fmi2Status)
+
     def _fmi2Function(self, fname, argnames, argtypes, restype):
 
         if not hasattr(self.dll, fname):
@@ -335,6 +341,27 @@ def deSerializeFMUstate(self, serializedState, state):
         buffer = create_string_buffer(serializedState)
         self.fmi2DeSerializeFMUstate(self.component, buffer, len(buffer), byref(state))
 
+    def getDirectionalDerivative(self, vUnknown_ref, vKnown_ref, dvKnown):
+        """ Get the partial derivative
+
+        Parameters:
+            vUnknown_ref    a list of value references of the unknowns
+            vKnown_ref      a list of value references of the knowns
+            dvKnown         a list of delta values (one per known)
+
+        Returns:
+            a list of the partial derivatives (one per unknown)
+        """
+
+        vUnknown_ref = (fmi2ValueReference * len(vUnknown_ref))(*vUnknown_ref)
+        vKnown_ref = (fmi2ValueReference * len(vKnown_ref))(*vKnown_ref)
+        dvKnown = (fmi2Real * len(dvKnown))(*dvKnown)
+        dvUnknown = (fmi2Real * len(vUnknown_ref))()
+
+        self.fmi2GetDirectionalDerivative(self.component, vUnknown_ref, len(vUnknown_ref), vKnown_ref, len(vKnown_ref), dvKnown, dvUnknown)
+
+        return list(dvUnknown)
+
 
 class FMU2Model(_FMU2):
     """ Base class for FMI 2.0 model exchange FMUs """
diff --git a/tests/test_get_directional_derivative.py b/tests/test_get_directional_derivative.py
new file mode 100644
index 00000000..7f99f65f
--- /dev/null
+++ b/tests/test_get_directional_derivative.py
@@ -0,0 +1,63 @@
+import unittest
+from shutil import rmtree
+from unittest import skipIf
+
+from fmpy import platform, read_model_description, extract
+from fmpy.util import download_test_file
+from fmpy.fmi2 import FMU2Slave
+
+
+class GetDirectionalDerivativeTest(unittest.TestCase):
+
+    @skipIf(platform not in ['win32', 'win64'], "Current platform not supported by this FMU")
+    def test_get_directional_derivative(self):
+
+        fmu_filename = 'Rectifier.fmu'
+
+        download_test_file('2.0', 'CoSimulation', 'Dymola', '2017', 'Rectifier', fmu_filename)
+
+        model_description = read_model_description(filename=fmu_filename)
+
+        unzipdir = extract(fmu_filename)
+
+        fmu = FMU2Slave(guid=model_description.guid,
+                        unzipDirectory=unzipdir,
+                        modelIdentifier=model_description.coSimulation.modelIdentifier)
+
+        fmu.instantiate()
+        fmu.setupExperiment()
+        fmu.enterInitializationMode()
+
+        # get the partial derivative for an initial unknown
+        unknown = model_description.initialUnknowns[1]
+
+        self.assertEqual('iAC[1]', unknown.variable.name)
+
+        vrs_unknown = [unknown.variable.valueReference]
+        vrs_known = [v.valueReference for v in unknown.dependencies]
+        dv_known = [1.0] * len(unknown.dependencies)
+
+        partial_der = fmu.getDirectionalDerivative(vUnknown_ref=vrs_unknown, vKnown_ref=vrs_known, dvKnown=dv_known)
+
+        self.assertEqual([-2.0], partial_der)
+
+        fmu.exitInitializationMode()
+
+        # get the partial derivative for three output variables
+        unknowns = model_description.outputs[4:7]
+
+        self.assertEqual(['uAC[1]', 'uAC[2]', 'uAC[3]'], [u.variable.name for u in unknowns])
+
+        vrs_unknown = [u.variable.valueReference for u in unknowns]
+        vrs_known = [v.valueReference for v in unknowns[0].dependencies]
+        dv_known = [1.0] * len(vrs_known)
+
+        partial_der = fmu.getDirectionalDerivative(vUnknown_ref=vrs_unknown, vKnown_ref=vrs_known, dvKnown=dv_known)
+
+        self.assertAlmostEqual(-1500, partial_der[0])
+        self.assertAlmostEqual(0, partial_der[1])
+        self.assertAlmostEqual(1500, partial_der[2])
+
+        fmu.terminate()
+        fmu.freeInstance()
+        rmtree(unzipdir)