From aec37b6720df18d5e6dc6bba1a83064dd42735b1 Mon Sep 17 00:00:00 2001
From: Arthur Drobot <drobotarthur@gmail.com>
Date: Thu, 27 Jul 2017 10:03:26 -0700
Subject: [PATCH] Add absolute value function to standard plugin. Modify
 getNTermsExp to work on negative exponents instead (and correctly).

---
 .../nwapw/abacus/plugin/StandardPlugin.java   | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/org/nwapw/abacus/plugin/StandardPlugin.java b/src/org/nwapw/abacus/plugin/StandardPlugin.java
index 9881ff2..ac4eb76 100755
--- a/src/org/nwapw/abacus/plugin/StandardPlugin.java
+++ b/src/org/nwapw/abacus/plugin/StandardPlugin.java
@@ -75,6 +75,7 @@ public class StandardPlugin extends Plugin {
         });
 
         registerFunction("!", new Function() {
+            //private ArrayLi
             @Override
             protected boolean matchesParams(NumberInterface[] params) {
                 return params.length == 1;
@@ -95,6 +96,18 @@ public class StandardPlugin extends Plugin {
             }
         });
 
+        registerFunction("abs", new Function() {
+            @Override
+            protected boolean matchesParams(NumberInterface[] params) {
+                return params.length == 1;
+            }
+
+            @Override
+            protected NumberInterface applyInternal(NumberInterface[] params) {
+                return params[0].multiply((new NaiveNumber(params[0].signum())).promoteTo(params[0].getClass()));
+            }
+        });
+
         registerFunction("exp", new Function() {
             @Override
             protected boolean matchesParams(NumberInterface[] params) {
@@ -126,14 +139,15 @@ public class StandardPlugin extends Plugin {
      * @return
      */
     private int getNTermsExp(NumberInterface maxError, NumberInterface x){
-        //We need n such that x^(n+2) <= (n+1)! * maxError
+        //We need n such that |x^(n+1)| <= (n+1)! * maxError
         //The variables LHS and RHS refer to the above inequality.
         int n = 0;
-        NumberInterface LHS = x.intPow(2), RHS = maxError;
+        x = this.getFunction("abs").apply(x);
+        NumberInterface LHS = x, RHS = maxError;
         while(LHS.compareTo(RHS) > 0){
             n++;
             LHS = LHS.multiply(x);
-            RHS = RHS.multiply(new NaiveNumber(n).promoteTo(RHS.getClass()));
+            RHS = RHS.multiply(new NaiveNumber(n+1).promoteTo(RHS.getClass()));
         }
         return n;
     }