Revised ResourcePrice class and methods. Added tests for problem...

Revised ResourcePrice class and methods. Added tests for problem simplification routines. Started problem identification method.

src/topupopt/data/finance/utils.py

+# *****************************************************************************
+# *****************************************************************************
+
+from ...problems.esipp.network import Arcs
+
+# *****************************************************************************
+# *****************************************************************************
+
+class ArcInvestments(Arcs):
+    """A class for defining arcs linked to investments."""
+
+    # *************************************************************************
+    # *************************************************************************
+
+    def __init__(self, investments: tuple, **kwargs):
+        # keep investment data
+        self.investments = investments
+        # initialise object
+        Arcs.__init__(
+            self,
+            minimum_cost=tuple([inv.net_present_value() for inv in self.investments]),
+            # validate=False,
+            **kwargs
+        )
+
+    # *************************************************************************
+    # *************************************************************************
+
+    def update_minimum_cost(self):
+        "Updates the minimum costs using the Investment objects."
+        self.minimum_cost = tuple([inv.net_present_value() for inv in self.investments])
+
+    # *************************************************************************
+    # *************************************************************************
+
+# *****************************************************************************
+# *****************************************************************************
\ No newline at end of file