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rupee aims to provide user-friendly tools for use in financial gems and applications.
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README.md

Rupee - financial tools for Ruby

Homepage www.brymck.com
Author Bryan McKelvey
Copyright (c) 2011 Bryan McKelvey
License MIT

Flattr this git repo

    /|\
   / | \
  /  |  \
 /_ / \ _\    RU       PE      E
|  |   |  |   _ _      _
|  |   |  |  | | |    | |__o  ____
|  |   |  |  | | | _  |  __| |____|
| _|   |_ |  | | |/ / | |___
 \  \ /  /  /_/|___/   \____|
  \  |  /
   \ | /
    \|/ brymck

Installing

Note that you must have Ruby 1.8.7+ installed and the ability to compile native extensions (standard on most platforms and available on Windows via DevKit).

gem install rupee

You can also do things the hard way if you want to keep track of the repo:

git clone git://github.com/brymck/rupee.git
cd rupee
bundle update
rake install

After all that hard work, you can take a test drive by running something like this in the Ruby console (i.e. irb in a command prompt):

require "rupee"
Rupee::Option.black_scholes "c", 60, 65, 0.25, 0.08, 0, 0.3
Rupee::Call.new(
  :underlying => 60,
  :strike     => 65,
  :time       =>  0.25,
  :rate       =>  0.08,
  :div_yield  =>  0.00,
  :volatility =>  0.3
).black_scholes

both of which should return 2.1334.

You should also be able to get the latest stock info for, for example, Wells Fargo using the following (note that you only need to require the quote module):

require "rupee/quote"
wfc = Rupee::Quote.new("WFC")

wfc.get :price, :change, :pct_change
#=> {:price=>24.96, :change=>0.17, :pct_change =>0.686}

wfc.price
#=> 24.96

wfc.change
#=> 0.17

wfc.get will return a hash of the requested information for the security. Each valid parameter will also have its own utility method. The results will update every wfc.frequency seconds (defaults to 15).

Got it? Good. This will surely help you collect some rupees in real life.

Performance

This is just a simple benchmark I ran on my own laptop, where I value a simple call option with Black-Scholes 100,000 times. You can test the same on yours with rake, but in any case it makes the point that for the mathematical side of finance a native extension has substantial benefits:

rake benchmark:black_scholes

Results:

                          user     system      total        real
Rupee (class):        0.190000   0.000000   0.190000 (  0.194001)
Rupee (one object):   0.180000   0.000000   0.180000 (  0.183091)
Rupee (new object):   2.210000   0.000000   2.210000 (  2.213351)
Pure Ruby:            2.320000   0.000000   2.320000 (  2.324259)

In words, for math-intensive operations, using a C implementation is clearly faster than the same thing in Ruby.

Also, if you're doing a valuation on a one-off set of examples (e.g. in a Monte Carlo simulation), you probably don't want to create an object every time. Something like Rupee::Option.black_scholes ... should work just fine. Creating a Rupee::Option object takes roughly the same amount of time as running Rupee::Option.black_scholes a dozen times.

However, if you're creating and reusing an object, I strongly recommend preserving the object orientation of Ruby: the penalty for using a new instance rather than calling the class method directly is almost entirely in the object initialization itself.

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