### Install FastXirr Gem via CLI

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Command to install the FastXirr gem directly from RubyGems using the command-line interface. This is useful for quick setup or testing outside of a project's Gemfile.

--------------------------------

### Test FastXirr Gem

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Instructions for running the test suite for the FastXirr gem. This requires installing development dependencies via Bundler and then executing the tests using the `rake` command.

```bash
bundle install
rake test
```

--------------------------------

### Install FastXirr Gem via RubyGems

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Instructions for adding the FastXirr gem to your project's Gemfile and installing it using Bundler. This is the standard method for integrating the gem into a Ruby application.

```ruby
gem 'fast_xirr'
```

```bash
bundle install
```

--------------------------------

### Build FastXirr Gem from Source

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Steps to build the FastXirr gem from its source code. This involves cloning the repository, building the gem file using the gemspec, and then installing the local gem file.

```bash
git clone https://github.com/fintual-oss/fast-xirr.git
cd fast_xirr
gem build fast_xirr.gemspec
# This will create a .gem file, e.g., fast_xirr-1.x.x.gem
gem install ./fast_xirr*.gem
```

--------------------------------

### Configure XIRR Calculation Options

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Illustrates how to customize XIRR calculations by setting tolerance (`tol`), maximum iterations (`max_iter`), and the initial bracket interval (`initial_bracket`) for Brent's method. These parameters can help improve convergence or performance.

```ruby
require 'fast_xirr'
require 'date'

cashflows = [
  [1000, Date.new(1985, 1, 1)],
  [-600, Date.new(1990, 1, 1)],
  [-6000, Date.new(1995, 1, 1)]
]

result = FastXirr.calculate(cashflows: cashflows, tol: 1e-2, max_iter: 100)
puts "XIRR: #{result}"
# => XIRR: 0.22305878076614422

result = FastXirr.calculate(cashflows: cashflows, tol: 1e-8, max_iter: 2)
puts "XIRR: #{result}"
# => XIRR: NaN

# You can also specify the initial bracket (search interval) for Brent's method
result = FastXirr.calculate(
  cashflows: cashflows,
  initial_bracket: [-0.5, 5.0]
)
puts "XIRR: #{result}"
# => XIRR: 0.22568333743016633
```

--------------------------------

### Calculate XIRR with FastXirr

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Demonstrates the basic usage of the FastXirr gem to calculate the Extended Internal Rate of Return (XIRR) for a given set of cash flows and dates. The cash flows are provided as an array of [amount, date] pairs.

```ruby
require 'fast_xirr'
require 'date'

cashflows = [
  [1000, Date.new(1985, 1, 1)],
  [-600, Date.new(1990, 1, 1)],
  [-6000, Date.new(1995, 1, 1)]
]

result = FastXirr.calculate(cashflows: cashflows)
puts "XIRR: #{result}"
# => XIRR: 0.22568401743016633
```

--------------------------------

### Handle XIRR Calculation Failure (NaN)

Source: https://github.com/fintual-oss/fast-xirr/blob/main/README.md

Shows how FastXirr handles cases where a solution cannot be found, returning `nan`. It also demonstrates how to check if the result is `nan` using the `.nan?` method.

```ruby
require 'fast_xirr'
require 'date'

result = FastXirr.calculate(cashflows: [[1000, Date.new(1985, 1, 1)]])

puts "XIRR: #{result}"
# => XIRR: NaN

result.nan?
# => true
```

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