add finance module with net_present_value function

Author: gabrielaznar

climada/util/finance.py

@@ -0,0 +1,28 @@
+"""
+Finance functionalities.
+"""
+import logging
+
+LOGGER = logging.getLogger(__name__)
+
+def net_present_value(years, disc_rates, val_years):
+    """Compute net present value.
+
+    Parameters:
+        years (np.array): array with the sequence of years to consider.
+        disc_rates (np.array): discount rate for every year in years.
+        val_years (np.array): chash flow at each year.
+
+    Returns:
+        float
+    """
+    if years.size != disc_rates.size or years.size != val_years.size:
+        LOGGER.error('Wrong input sizes %s, %s, %s.', years.size,
+                     disc_rates.size, val_years.size)
+        raise ValueError
+
+    npv = val_years[-1]
+    for val, disc in zip(val_years[-2::-1], disc_rates[-2::-1]):
+        npv = val + npv/(1+disc)
+
+    return npv

climada/util/test/test_finance.py

@@ -0,0 +1,22 @@
+"""
+Test of finance module
+"""
+import unittest
+import numpy as np
+
+import climada.util.finance as u_fin
+
+class TestNetpresValue(unittest.TestCase):
+    """Test date functions """
+    def test_net_pres_val_pass(self):
+        """ Test net_present_value against MATLAB reference"""
+        years = np.arange(2018, 2041)
+        disc_rates = np.ones(years.size)*0.02
+        val_years = np.ones(years.size)*6.512201157564418e9
+        res = u_fin.net_present_value(years, disc_rates, val_years)
+        
+        self.assertEqual(1.215049630691397e+11, res)
+
+# Execute Tests
+TESTS = unittest.TestLoader().loadTestsFromTestCase(TestNetpresValue)
+unittest.TextTestRunner(verbosity=2).run(TESTS)