From e3220e822bb2cfbb80291259b05d63770409bdc6 Mon Sep 17 00:00:00 2001
From: Matthew McDermott <mattmcdermott8@gmail.com>
Date: Sat, 19 Mar 2016 10:45:09 -0700
Subject: [PATCH 1/3] Adding two new, fast methods for IRR.

---
 finance.js | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/finance.js b/finance.js
index f186b07..0931f9c 100755
--- a/finance.js
+++ b/finance.js
@@ -48,6 +48,52 @@ Finance.prototype.IRR = function(cfs) {
   return Math.round(bestGuess * 100) / 100;
 };
 
+function seekZero(fn) {
+  var x = 0;
+  while (fn(x) > 0) {
+    x += 1;
+  }
+  while (fn(x) < 0) {
+    x -= 0.01
+  }
+  return x + 0.01;
+}
+
+function seekZeroD(fn, d) {
+  var x = 0;
+  var y = fn(x);
+  while (Math.abs(y) > 0.0001) {
+    x -= y/d(x)
+    y = fn(x);
+  }
+  return x;
+}
+
+// Internal Rate of Return (IRR)
+Finance.prototype.IRRFast = function(cfs) { 
+
+  var args = arguments;
+  function npv(rate) {
+    var rrate = (1 + rate/100);
+    var npv = args[0];
+    for (var i = 1; i < args.length; i++) {
+      npv += (args[i] / Math.pow(rrate, i));
+    }
+    return npv;
+  }
+
+  function npvp(rate) {
+    var rrate = (1+rate/100);
+    var npvp = 0
+    for (var i = 1; i < args.length; i++) {
+      npvp -= (args[i]/Math.pow(rrate, i+1))*(1/100)
+    }
+    return npvp
+  }
+
+  return seekZeroD(npv, npvp);
+};
+
 // Payback Period (PP)
 Finance.prototype.PP = function(numOfPeriods, cfs) {
   // for even cash flows

From db6ff9f2585a45bd8600b3d66227b8a0ed7b181b Mon Sep 17 00:00:00 2001
From: Matthew McDermott <mattmcdermott8@gmail.com>
Date: Sun, 20 Mar 2016 11:05:37 -0700
Subject: [PATCH 2/3] This version takes ~0.2 seconds for 50k iterations, vs.
 ~15 seconds with the old version.

---
 finance.js  | 48 ++++--------------------------------------------
 testFast.js |  9 +++++++++
 2 files changed, 13 insertions(+), 44 deletions(-)
 create mode 100644 testFast.js

diff --git a/finance.js b/finance.js
index 0931f9c..1cb6a27 100755
--- a/finance.js
+++ b/finance.js
@@ -28,28 +28,9 @@ Finance.prototype.NPV = function (rate) {
   return Math.round(npv * 100) / 100;
 };
 
-// Internal Rate of Return (IRR)
-Finance.prototype.IRR = function(cfs) { 
-  var bestGuess, currentNPV;
-  var checkNPV = function(rate, arguments){
-    var npv = arguments[0];
-    // base case
-    for (var i = 1; i < arguments.length; i++) {
-      npv +=(arguments[i] / Math.pow((1 + rate/100), i));
-    }
-    currentNPV = Math.round(npv * 100) / 100;
-    if (currentNPV <= 0) {
-      bestGuess = rate;
-      return;
-    } 
-    checkNPV(rate + 0.01, arguments);
-  }; 
-  checkNPV(0.01, arguments);
-  return Math.round(bestGuess * 100) / 100;
-};
-
+// seekZero seeks the zero point of the function fn(x), accurate to within x \pm 0.01. fn(x) must be decreasing with x.
 function seekZero(fn) {
-  var x = 0;
+  var x = 1;
   while (fn(x) > 0) {
     x += 1;
   }
@@ -59,19 +40,8 @@ function seekZero(fn) {
   return x + 0.01;
 }
 
-function seekZeroD(fn, d) {
-  var x = 0;
-  var y = fn(x);
-  while (Math.abs(y) > 0.0001) {
-    x -= y/d(x)
-    y = fn(x);
-  }
-  return x;
-}
-
 // Internal Rate of Return (IRR)
-Finance.prototype.IRRFast = function(cfs) { 
-
+Finance.prototype.IRR = function(cfs) { 
   var args = arguments;
   function npv(rate) {
     var rrate = (1 + rate/100);
@@ -81,17 +51,7 @@ Finance.prototype.IRRFast = function(cfs) {
     }
     return npv;
   }
-
-  function npvp(rate) {
-    var rrate = (1+rate/100);
-    var npvp = 0
-    for (var i = 1; i < args.length; i++) {
-      npvp -= (args[i]/Math.pow(rrate, i+1))*(1/100)
-    }
-    return npvp
-  }
-
-  return seekZeroD(npv, npvp);
+  return Math.round(seekZero(npv) * 100) / 100;
 };
 
 // Payback Period (PP)
diff --git a/testFast.js b/testFast.js
new file mode 100644
index 0000000..9eeaa2b
--- /dev/null
+++ b/testFast.js
@@ -0,0 +1,9 @@
+var Finance = require('./finance.js')
+
+var finance = new Finance();
+
+for (var i = 0; i < 50000; i++) {
+  finance.IRR(-500000, 200000, 300000, 200000)
+}
+
+console.log(finance.IRR(-500000, 200000, 300000, 200000))

From 96aeb8d597527f96663024c7c3a4a0744002a744 Mon Sep 17 00:00:00 2001
From: Matthew McDermott <mattmcdermott8@gmail.com>
Date: Sun, 20 Mar 2016 11:05:47 -0700
Subject: [PATCH 3/3] Removing test code.

---
 testFast.js | 9 ---------
 1 file changed, 9 deletions(-)
 delete mode 100644 testFast.js

diff --git a/testFast.js b/testFast.js
deleted file mode 100644
index 9eeaa2b..0000000
--- a/testFast.js
+++ /dev/null
@@ -1,9 +0,0 @@
-var Finance = require('./finance.js')
-
-var finance = new Finance();
-
-for (var i = 0; i < 50000; i++) {
-  finance.IRR(-500000, 200000, 300000, 200000)
-}
-
-console.log(finance.IRR(-500000, 200000, 300000, 200000))