[lmi-commits] [lmi] master be56aad 2/8: Move and rename a present-value function

[Greg Chicares]

branch: master
commit be56aad761518b1946d99cd5dcd7bb29b2f5bed4
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Move and rename a present-value function
    
    Precise usage differentiates NPV from PV; this is PV. It was used
    nowhere except in the unit test, and is not suitable for general use.
---
 financial.hpp      | 23 -----------------------
 financial_test.cpp | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/financial.hpp b/financial.hpp
index 538dcf2..7e7284b 100644
--- a/financial.hpp
+++ b/financial.hpp
@@ -70,29 +70,6 @@ long double fv
 }
 
 template<typename InputIterator>
-long double npv
-    (InputIterator first
-    ,InputIterator last
-    ,long double i
-    )
-{
-    if(first == last)
-        {
-        return 0.0L;
-        }
-    long double const v = 1.0L / (1.0L + i);
-    long double vn = 1.0L;
-    long double z = *first;
-    InputIterator j = first;
-    while(++j != last)
-        {
-        vn *= v;
-        z += *j * vn;
-        }
-    return z;
-}
-
-template<typename InputIterator>
 class irr_helper
 {
   public:
diff --git a/financial_test.cpp b/financial_test.cpp
index 263d768..5bf881c 100644
--- a/financial_test.cpp
+++ b/financial_test.cpp
@@ -33,6 +33,36 @@
 #include <iostream>
 #include <vector>
 
+/// Present value, for local use only--beware division by zero.
+///
+/// This could be reimplemented in terms of i rather than v for
+/// general use. The problem with using v is that i can easily
+/// be -100%, in which case v=1/(1+i)=1/0, but it is preferable
+/// to avoid division by zero.
+
+template<typename InputIterator>
+long double pv
+    (InputIterator first
+    ,InputIterator last
+    ,long double i
+    )
+{
+    if(first == last)
+        {
+        return 0.0L;
+        }
+    long double const v = 1.0L / (1.0L + i);
+    long double vn = 1.0L;
+    long double z = *first;
+    InputIterator j = first;
+    while(++j != last)
+        {
+        vn *= v;
+        z += *j * vn;
+        }
+    return z;
+}
+
 void mete_0
     (std::vector<double> const& payments
     ,std::vector<double> const& benefits
@@ -145,10 +175,10 @@ int test_main(int, char*[])
     // This NPV is -9.777068044058979E-12 in a gnumeric spreadsheet,
     // versus -9.86988e-014 with MinGW-w64 gcc-6.3.0; the 1e-13
     // tolerance is simply the materially_equal() default.
-    LMI_TEST(std::fabs(npv(q.begin(), q.end(), results.back())) <= 1e-13);
+    LMI_TEST(std::fabs(pv(q.begin(), q.end(), results.back())) <= 1e-13);
 
     // Trivially, NPV at 0% interest is summation.
-    LMI_TEST(materially_equal(-4950.0L, npv(q.begin(), q.end(), 0.0)));
+    LMI_TEST(materially_equal(-4950.0L, pv(q.begin(), q.end(), 0.0)));
 
     // Test const vectors.
     std::vector<double> const cp(p);