Project

## apy

0.0
The project is in a healthy, maintained state
Helpers for calculating various interest scenarios
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Popularity
Development
Primary Language
Ruby
MIT

# Apy

Various helpers for calculating interest

## TODO

• Amortization
• Update method signatures to only use day counts
• Comprehensive examples w/ tests
• Setup ci

## Installation

`gem "apy"`

And then execute:

``````\$ bundle install
``````

Or install it yourself as:

``````\$ gem install apy
``````

## Usage

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

### As a Module

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

#### `weighted_harmonic_mean`

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:

Amount invested Share price
1000 156.23
1000 156.30
1000 173.15
1000 188.72
1000 204.61
1000 178.23

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

Given the following:

Amount invested Share price
500 200.00
1000 100.00

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```

#### `compound`

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`

#### `dca_compound`

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

## Development

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.

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/fire-pls/apy.