MAINT: fix unit conversion (#174)

The original unit conversion done in propagate_data_changes (scimath.units.quantity) can cause conversion error. This PR adds a fix and test for that. closes issue #171 --------- Co-authored-by: Chengyu Liu <[email protected]>
enthought · Mar 22, 2023 · 49468e0 · 49468e0
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commit 49468e0
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Showing 2 changed files with 10 additions and 2 deletions.
diff --git a/scimath/units/quantity.py b/scimath/units/quantity.py
@@ -303,8 +303,7 @@ def propagate_data_changes(self):
             return
 
         # Replace the predecessor's data with converted data.
-        new_quantity = self.change_unit_system(predecessor.units)
-        predecessor.data = new_quantity.data
+        predecessor.data = units_convert(self.data, self.units, predecessor.units)
 
         # Recursively continue propagating.
         predecessor.propagate_data_changes()

diff --git a/scimath/units/tests/test_units.py b/scimath/units/tests/test_units.py
@@ -197,6 +197,15 @@ def test_propagation(self):
         self.assertAlmostEqual(30., q1.data, 1,
                                "Propagation test expected data 30, got %s" % str(q1.data))
 
+    def test_propagation_to_imperial(self):
+        """ Tests data propagation for a single converted quantity. """
+
+        q1 = Quantity(10.0, units='ft', family_name='depth')
+        q2 = q1.change_unit_system('METRIC')
+        q2.data = 2 * q2.data
+        q2.propagate_data_changes()
+        self.assertAlmostEqual(q1.data, 20.0)
+
     def test_get_original(self):
 
         q1 = Quantity(10, units='m', family_name='depth')