MAINT: clean up the implementation of fv

In particular, more clearly divide the rate-is-zero versus
rate-is-nonzero cases. Also organize the tests and add test cases for
broadcasting and zero rate.

Author: person142

numpy_financial/_financial.py

@@ -124,11 +124,28 @@ def fv(rate, nper, pmt, pv, when='end'):
 
     """
     when = _convert_when(when)
-    (rate, nper, pmt, pv, when) = map(np.asarray, [rate, nper, pmt, pv, when])
-    temp = (1+rate)**nper
-    fact = np.where(rate == 0, nper,
-                    (1 + rate*when)*(temp - 1)/rate)
-    return -(pv*temp + pmt*fact)
+    rate, nper, pmt, pv, when = np.broadcast_arrays(rate, nper, pmt, pv, when)
+
+    fv_array = np.empty_like(rate)
+    zero = rate == 0
+    nonzero = ~zero
+
+    fv_array[zero] = -(pv[zero] + pmt[zero] * nper[zero])
+
+    rate_nonzero = rate[nonzero]
+    nper_nonzero = nper[nonzero]
+    temp = (1 + rate_nonzero)**nper[nonzero]
+    fv_array[nonzero] = (
+        -pv[nonzero] * temp
+        - pmt[nonzero] * (1 + rate_nonzero * when[nonzero]) / rate_nonzero
+        * (temp - 1)
+    )
+
+    if np.ndim(fv_array) == 0:
+        # Follow the ufunc convention of returning scalars for scalar
+        # and 0d array inputs.
+        return fv_array.item(0)
+    return fv_array
 
 
 def pmt(rate, nper, pv, fv=0, when='end'):

numpy_financial/tests/test_financial.py

@@ -55,14 +55,6 @@ def test_pv_decimal(self):
                             Decimal('0')),
                      Decimal('-127128.1709461939327295222005'))
 
-    def test_fv(self):
-        assert_equal(npf.fv(0.075, 20, -2000, 0, 0), 86609.362673042924)
-
-    def test_fv_decimal(self):
-        assert_equal(npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            0, 0),
-                     Decimal('86609.36267304300040536731624'))
-
     def test_pmt(self):
         res = npf.pmt(0.08 / 12, 5 * 12, 15000)
         tgt = -304.145914
@@ -197,15 +189,6 @@ def test_when(self):
         assert_equal(npf.pv(0.07, 20, 12000, 0, 0),
                      npf.pv(0.07, 20, 12000, 0, 'end'))
 
-        # begin
-        assert_equal(npf.fv(0.075, 20, -2000, 0, 1),
-                     npf.fv(0.075, 20, -2000, 0, 'begin'))
-        # end
-        assert_equal(npf.fv(0.075, 20, -2000, 0),
-                     npf.fv(0.075, 20, -2000, 0, 'end'))
-        assert_equal(npf.fv(0.075, 20, -2000, 0, 0),
-                     npf.fv(0.075, 20, -2000, 0, 'end'))
-
         # begin
         assert_equal(npf.pmt(0.08 / 12, 5 * 12, 15000., 0, 1),
                      npf.pmt(0.08 / 12, 5 * 12, 15000., 0, 'begin'))
@@ -267,21 +250,6 @@ def test_decimal_with_when(self):
                      npf.pv(Decimal('0.07'), Decimal('20'), Decimal('12000'),
                             Decimal('0'), 'end'))
 
-        # begin
-        assert_equal(npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0'), Decimal('1')),
-                     npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0'), 'begin'))
-        # end
-        assert_equal(npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0')),
-                     npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0'), 'end'))
-        assert_equal(npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0'), Decimal('0')),
-                     npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'),
-                            Decimal('0'), 'end'))
-
         # begin
         assert_equal(npf.pmt(Decimal('0.08') / Decimal('12'),
                              Decimal('5') * Decimal('12'), Decimal('15000.'),
@@ -475,3 +443,80 @@ def test_decimal_broadcasting(self):
             Decimal('2000')
         )
         assert_almost_equal(result, desired, decimal=4)
+
+
+class TestFv:
+    def test_float(self):
+        assert_allclose(
+            npf.fv(0.075, 20, -2000, 0, 0),
+            86609.362673042924,
+            rtol=1e-10,
+        )
+
+    def test_decimal(self):
+        assert_almost_equal(
+            npf.fv(Decimal('0.075'), Decimal('20'), Decimal('-2000'), 0, 0),
+            Decimal('86609.36267304300040536731624'),
+            decimal=10,
+        )
+
+    @pytest.mark.parametrize('when', [1, 'begin'])
+    def test_when_is_begin_float(self, when):
+        assert_allclose(
+            npf.fv(0.075, 20, -2000, 0, when),
+            93105.064874,  # Computed using Google Sheet's FV
+            rtol=1e-10,
+        )
+
+    @pytest.mark.parametrize('when', [Decimal('1'), 'begin'])
+    def test_when_is_begin_decimal(self, when):
+        result = npf.fv(
+            Decimal('0.075'),
+            Decimal('20'),
+            Decimal('-2000'),
+            Decimal('0'),
+            when,
+        )
+        assert_almost_equal(result, Decimal('93105.064874'), decimal=5)
+
+    @pytest.mark.parametrize('when', [None, 0, 'end'])
+    def test_when_is_end_float(self, when):
+        args = (0.075, 20, -2000, 0)
+        if when is None:
+            result = npf.fv(*args)
+        else:
+            result = npf.fv(*args, when)
+        assert_allclose(
+            result,
+            86609.362673,  # Computed using Google Sheet's FV
+            rtol=1e-10,
+        )
+
+    @pytest.mark.parametrize('when', [None, Decimal('0'), 'end'])
+    def test_when_is_end_decimal(self, when):
+        args = (
+            Decimal('0.075'),
+            Decimal('20'),
+            Decimal('-2000'),
+            Decimal('0'),
+        )
+        if when is None:
+            result = npf.fv(*args)
+        else:
+            result = npf.fv(*args, when)
+        assert_almost_equal(result, Decimal('86609.362673'), decimal=5)
+
+    def test_broadcast(self):
+        result = npf.fv([[0.1], [0.2]], 5, 100, 0, [0, 1])
+        # All values computed using Google Sheet's FV
+        desired = [[-610.510000, -671.561000],
+                   [-744.160000, -892.992000]]
+        assert_allclose(result, desired, rtol=1e-10)
+
+    def test_some_rates_zero(self):
+        # Check that the logical indexing is working correctly.
+        assert_allclose(
+            npf.fv([0, 0.1], 5, 100, 0),
+            [-500, -610.51],  # Computed using Google Sheet's FV
+            rtol=1e-10,
+        )