Added PointValue class

docs/source/api/exports.rst

@@ -31,6 +31,10 @@ Exports
     :members:
     :show-inheritance:
 
+.. autoclass:: PointValue
+    :members:
+    :show-inheritance:
+
 .. autoclass:: AverageSurface
     :members:
     :show-inheritance:

festim/__init__.py

@@ -78,6 +78,7 @@
 from .exports.derived_quantities.total_surface import TotalSurface
 from .exports.derived_quantities.total_volume import TotalVolume
 from .exports.derived_quantities.average_surface import AverageSurface
+from .exports.derived_quantities.point_value import PointValue
 
 from .exports.derived_quantities.derived_quantities import DerivedQuantities
 

festim/exports/derived_quantities/point_value.py

@@ -0,0 +1,19 @@
+from festim import DerivedQuantity
+
+
+class PointValue(DerivedQuantity):
+    """DerivedQuantity relative to a point
+
+    Args:
+        field (str, int):  the field ("solute", 0, 1, "T", "retention")
+        point (int, float, list): the point coordinates
+    """
+
+    def __init__(self, field: str or int, x: float or list) -> None:
+        super().__init__(field)
+        self.x = x
+        self.title = "{} value at {}".format(field, x)
+
+    def compute(self):
+        """The value at the point"""
+        return self.function(self.x)

test/unit/test_exports/test_derived_quantities/test_point_value.py

@@ -0,0 +1,34 @@
+from festim import PointValue
+import fenics as f
+import pytest
+
+
+def test_title_H():
+    x = 1
+    field = "solute"
+    my_value = PointValue(field, x)
+    assert my_value.title == "{} value at {}".format(field, x)
+
+
+def test_title_T():
+    x = 1
+    field = "T"
+    my_value = PointValue(field, x)
+    assert my_value.title == "{} value at {}".format(field, x)
+
+
+class TestCompute:
+    mesh = f.UnitIntervalMesh(10)
+    V = f.FunctionSpace(mesh, "P", 1)
+
+    c = f.interpolate(f.Expression("x[0]", degree=1), V)
+
+    x = 1
+    my_value = PointValue("solute", x)
+    my_value.function = c
+
+    def test_minimum(self):
+        expected = self.c(self.x)
+
+        produced = self.my_value.compute()
+        assert produced == expected