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"Valentine's Day Equation" plotted in Ruby

#ruby #gnuplot #graphs #valentinesday

I'm trying to expose my kids to programming bit by bit. 😄 Things that work the best are something that they relate to. Almost right on cue, this blog post came up on my feed on dev.to on Saturday and I thought it would be a fun activity to help kids make Valentines in a new way. Thank you, @DevLorenz0 for the formula! ❤️

All you need is ruby & gnuplot, and possibly gnuplot official docs pdf if you want to experiment further.

# on Mac brew install gnuplot gem install gnuplot # Chocolotey has a package for Windows # choco install gnuplot  # Use rpm / apt on Linux # apt-get install gnuplot
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Code 

# valentine_day_plot.rb # Tested on Ruby 2.7.2 require 'rubygems' require 'gnuplot' valentines_day_function = lambda { |t| x = 16 * Math.sin(t)**3 y = 13 * Math.cos(t) - 5 * Math.cos(2 * t) - 2 * Math.cos(3 * t) - Math.cos(4 * t) # Experimentally found that rounding to 4  # produces the best results for us  [x.round(4).to_f, y.round(4).to_f] } # Adjust this to get more or less number of plot points # At the end we transpose array, to shape data for  # Gnuplot::DataSet input below DISTANCE_BETWEEN_POINTS = 0.0001 COORDINATES = (0..(2 * Math::PI)).step(DISTANCE_BETWEEN_POINTS) .to_a .map do |t| valentines_day_function.call(t) end.transpose Gnuplot.open do |gp| Gnuplot::Plot.new(gp) do |plot| plot.output 'valentine_day_plot.pdf' # Sized as a nice square to be printed on a A4 or US Letter page plot.terminal 'pdf colour size 8in,8in' # The following is self-explanatory, but setting range too small, # will put the graph out of bounds plot.xrange '[-20:20]' plot.yrange '[-20:20]' plot.title "Valentine's Day Equation" plot.ylabel 'Love-y' plot.xlabel 'Love-x' # DataSet.new can also take the formula directly, not just an array # of shape [x-coordinates, y-coordinates] plot.data << Gnuplot::DataSet.new(COORDINATES) do |ds| # You can also draw graph using variaous other types, # 'linespoints','steps','fillsteps', etc # See http://www.gnuplot.info/docs_5.4/Gnuplot_5_4.pdf  # for full docs ds.with = 'lines' ds.linewidth = 15 # Change this to the name of your Valentine ds.title = 'My Valentine' end end end
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Result

Valentine Day Graph plotted with lines

Here is an example of the plotted graph if we change DISTANCE_BETWEEN_POINTS = 0.1 and ds.with = 'steps' and ds.linewidth = 1
Valentine Day Graph plotted with steps

Bonus

PDF we generated above is perfect for printing, but if you wanted to convert it to an JPEG or PNG, you can use a graphics app like Photoshop or Gimp, or simply use imagemagick

# Install it if you don't have it brew install imagemagick convert -quality 300 -density 300 valentine_day_plot.pdf valentine_day_plot.jpg
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