Apy

Various helpers for calculating interest

• Comprehensive examples w/ tests
• Setup ci

Add this line to your application's Gemfile:

gem "apy"

And then execute:

$ bundle install

Or install it yourself as:

$ gem install apy

• As a module
  • Method: weighted_harmonic_mean
  • Method: compound
• Interest class
• Loan class

Apy::Calculable is the base module with the most exposed utility. Simply include it in a class which needs the functionality.

Link

Given a series of invested amounts, this can be used to effectively calculate the average share price, or DCA (dollar cost average) price of a position.

Given the following:

Investing a total of 6000 with the above share prices results in 174.57 for the average price paid per share.

Given the following:

Investing a total of 1500 with the above share prices results in 100.00 for the average price paid per share.

The module method accepts a matrix, with each array in the set having the following signature [invested_amount, share_price]:

dca = [
  [1000, 156.23],
  [1000, 156.30],
  [1000, 173.15],
  [1000, 188.72],
  [1000, 204.61],
  [1000, 178.23]
]
weighted_harmonic_mean(dca) == 174.5655590168175

Link

Simple compound interest formula. Variable names correspond to the following:

• principal The base amount before interest
• rate The expected interest rate
• times The number of times interest is calculated per term
• terms The number of terms to allow the principal accrue interest

Example: 1200@10% over 1y, interest paid monthly

compound(1200, rate: 0.1, times: 12, terms: 1) == 1325.66

A variant of #compound, wherein an amount is continually invested at varying interest rates. Similar to weighted_harmonic_mean, this method also accepts a matrix. The size of the matrix corresponds to the number of terms all funds will accrue.

Example: 1200@10% over 2y, interest paid monthly

dca = [
  [1200, 0.1],
  [1200, 0.1]
]
dca_compound(dca, times: 12) == 2790.125

todo

todo

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/0x5424/apy.

The gem is available as open source under the terms of the MIT License.