From 1c47181d1cdf9aa1aabe0c2769dc71fd524c3e16 Mon Sep 17 00:00:00 2001
From: "ali.hh.ramadhan@gmail.com" <ali.hh.ramadhan@gmail.com>
Date: Wed, 24 Mar 2021 21:24:52 -0400
Subject: [PATCH] Flesh out Compound interest problem

---
 .../templates/problems/compound-interest.html | 26 ++++++++++++-------
 .../templates/problems/plump-moose.html       |  2 +-
 src/static/code_stubs/c/compound_interest.c   |  4 +++
 src/static/code_stubs/c/plump_moose.c         |  4 +++
 .../javascript/compound_interest.js           |  4 +++
 .../code_stubs/julia/compound_interest.jl     |  4 +++
 .../code_stubs/python/compound_interest.py    |  4 +++
 src/static/visualization/compound-interest.js | 14 ++++++++--
 8 files changed, 49 insertions(+), 13 deletions(-)

diff --git a/src/problems/templates/problems/compound-interest.html b/src/problems/templates/problems/compound-interest.html
index dca02b0..1c31411 100644
--- a/src/problems/templates/problems/compound-interest.html
+++ b/src/problems/templates/problems/compound-interest.html
@@ -3,7 +3,7 @@
 {% load static %}
 
 {% block you_will_learn %}
-  cold moose are plump.
+  the most powerful force in the world according to Einstein. <sup>[<a href="https://quoteinvestigator.com/2019/09/09/interest/">citation needed</a>]</sup>
 {% endblock %}
 
 {% block problem_body %}
@@ -15,28 +15,31 @@
 <br>
 <p class="has-text-justified">
   If you start with an amount of money $m$ and the compound interest is calculated once a year with interest rate $r$
-  (as a fraction) then after $n$ years you end up with new amount $M$ given by
+  (as a fraction between 0 and 1) then after $n$ years you end up with a new amount $M$ given by
 
   $$ M = m (1 + r)^n $$
 </p>
 <br>
 
+This plot shows the growth of $m = 1,000$ dollars compounded every year at 10% ($r = 0.1$) for $n = 25$ years.
+
 <figure style="text-align: center;">
   <div id="compound-interest-figure"></id>
 </figure>
 <br>
 
 <p class="has-text-justified">
-  Submit some code with a function <tt>compound_interest(m, r, n)</tt> that computes $M$ given $m$, $r$, and $n$.
+  Submit some code with a function <tt>compound_interest(m, r, n)</tt> that computes the final amount $M$ after
+  starting with an amount $m$ compounded yearly at a rate $r$ for $n$ years.
 </p>
 {% endblock %}
 
 {% block input_description %}
-m, r, n
+Starting amount $m$, rate $r$, and number of years $n$.
 {% endblock %}
 
 {% block output_description %}
-M
+Final amount $M$.
 {% endblock %}
 
 {% block examples %}
@@ -45,8 +48,8 @@
     <p>Example</p>
   </div>
   <div class="message-body"
-       style="font-family: monospace; text-align: justify; word-wrap: break-word; white-space:pre;"><b>Input</b>: $1,000, 0.07, 25
-<b>Output</b>: $5,427.43</div>
+       style="font-family: monospace; text-align: justify; word-wrap: break-word; white-space:pre;"><b>Input</b>: 1000, 0.07, 25
+<b>Output</b>: 5427.43</div>
 </article>
 {% endblock %}
 
@@ -59,11 +62,14 @@
   <h3>Notes</h3>
   <ul>
     <li>
-      Compound interest was and is considered a kind of usury by many religions and even by Roman law.
+      Charging compound interest on loans was and is still considered a kind of <a href="https://en.wikipedia.org/wiki/Usury">usury</a>
+      by many religions and societies. The Romans and the Christian Bible condemn charging interest on loans to poor people as
+      it is seen as a form of exploitation. On the extreme end, Islam forbids the charging of any kind of interest as it sees borrowing
+      and lending as social transactions aimed at benefiting others and thus should not be profitable.
     </li>
     <li>
-      The number e was actually discovered by Jacob Bernoulli in 1683 when investigating compound interest.
-      Now of course called Euler's number because of Stigler's law.
+      The number $e$ was actually discovered by Jacob Bernoulli in 1683 when investigating compound interest.
+      Now of course called Euler's number because of <a href="https://en.wikipedia.org/wiki/Stigler%27s_law_of_eponymy">Stigler's law</a>.
     </li>
     <li>
       The <a href="https://en.wikipedia.org/wiki/Rule_of_72">Rule of 72</a> is a quick rule/approximation for figuring
diff --git a/src/problems/templates/problems/plump-moose.html b/src/problems/templates/problems/plump-moose.html
index 062d186..5b0c87e 100644
--- a/src/problems/templates/problems/plump-moose.html
+++ b/src/problems/templates/problems/plump-moose.html
@@ -3,7 +3,7 @@
 {% load static %}
 
 {% block you_will_learn %}
-  cold moose are plump.
+  cold moose have more fat
 {% endblock %}
 
 {% block problem_body %}
diff --git a/src/static/code_stubs/c/compound_interest.c b/src/static/code_stubs/c/compound_interest.c
index fa698a0..b5aed9e 100644
--- a/src/static/code_stubs/c/compound_interest.c
+++ b/src/static/code_stubs/c/compound_interest.c
@@ -1,3 +1,7 @@
 double compound_interest(double amount, double rate, int years) {
+    double new_amount = 0.0;
+
     // Your code goes here!
+
+    return new_amount;
 }
diff --git a/src/static/code_stubs/c/plump_moose.c b/src/static/code_stubs/c/plump_moose.c
index f6333b1..b2fb625 100644
--- a/src/static/code_stubs/c/plump_moose.c
+++ b/src/static/code_stubs/c/plump_moose.c
@@ -1,3 +1,7 @@
 double moose_body_mass(double latitude) {
+    double mass = 0.0;
+
     // Your code goes here!
+
+    return mass;
 }
diff --git a/src/static/code_stubs/javascript/compound_interest.js b/src/static/code_stubs/javascript/compound_interest.js
index 852d8f9..62213ed 100644
--- a/src/static/code_stubs/javascript/compound_interest.js
+++ b/src/static/code_stubs/javascript/compound_interest.js
@@ -1,3 +1,7 @@
 function compound_interest(amount, rate, years) {
+    var new_amount = 0
+
     // Your code goes here!
+
+    return new_amount
 }
diff --git a/src/static/code_stubs/julia/compound_interest.jl b/src/static/code_stubs/julia/compound_interest.jl
index b29dc2f..a5cae64 100644
--- a/src/static/code_stubs/julia/compound_interest.jl
+++ b/src/static/code_stubs/julia/compound_interest.jl
@@ -1,3 +1,7 @@
 function compound_interest(amount, rate, years)
+    new_amount = 0
+
     # Your code goes here!
+
+    return new_mount
 end
diff --git a/src/static/code_stubs/python/compound_interest.py b/src/static/code_stubs/python/compound_interest.py
index 40da619..9b2fb5f 100644
--- a/src/static/code_stubs/python/compound_interest.py
+++ b/src/static/code_stubs/python/compound_interest.py
@@ -1,2 +1,6 @@
 def compound_interest(amount, rate, years):
+    new_amount = 0
+
     # Your code goes here!
+
+    return new_amount
diff --git a/src/static/visualization/compound-interest.js b/src/static/visualization/compound-interest.js
index 7284d36..f843e91 100644
--- a/src/static/visualization/compound-interest.js
+++ b/src/static/visualization/compound-interest.js
@@ -1,3 +1,13 @@
+function visualize_test_case(input, output, expected, n) {
+    document.getElementById(`input${n}`).innerHTML =
+        `<b>Input</b>: m = ${input[0]}, r = ${input[1]}, n = ${input[2]} <br>`
+
+    document.getElementById(`output${n}`).innerHTML =
+        `<b>Output</b>: ${output[0]} (expected ${expected[0]}) <br>`
+
+    return
+}
+
 function compound_interest(amount, rate, years) {
     return amount * (1 + rate) ** years
 }
@@ -8,7 +18,7 @@ function make_compound_interest_figure() {
     var years = 25
 
     var year = new Array(years)
-    for (n = 1; n <= years; n++) {
+    for (n = 0; n <= years; n++) {
         year[n] = n
     }
 
@@ -31,4 +41,4 @@ function make_compound_interest_figure() {
     return
 }
 
-make_compound_interest_figure()
\ No newline at end of file
+make_compound_interest_figure()