GoalSeek

This gem implements a method similar to Microsoft Excel's GoalSeek macro. According to Microsoft, GoalSeek uses a simple linear search:

The Goal Seek command uses a simple linear search beginning with guesses on the positive or negative side of the value in the source cell (By Changing Cell). Excel uses the initial guesses and recalculates the formula. Whichever guess brings the formula result closer to the targeted result (To Value) is the direction (positive or negative) in which Goal Seek heads. If neither direction appears to approach the target value, Goal Seek makes additional guesses that are further away from the source cell. After the direction is determined, Goal Seek uses an iterative process in which the source cell is incremented or decremented at varying rates until the target value is reached.

Source: https://support.microsoft.com/en-us/help/100782/xl-method-used-by-goal-seek-to-find-a-solution

Add this line to your application's Gemfile:

gem 'goalseek'

And then execute:

$ bundle

Or install it yourself as:

$ gem install goalseek

This is a simple example of a linear search on a qubic function.

Bounds are automatically determined if they are within -10^10 to 10^10. Iterations are limited to 1000 by default.

begin
    goalseeker = GoalSeek::LinearSearch.new(Proc.new() { |x| x ** 3 });
    result = goalseeker.seek(27) # returns 3.0
rescue GoalSeek::InvalidBoundError
    puts "Function does not cross target value within interval (-10^10, 10^10)"
rescue GoalSeek::InvalidFunctionError
    puts "Provided block is not callable" 
end

For more examples, please have a look at the specs.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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 tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/pehlert/goalseek.

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