An algorithm to generate fake but realistic looking graph data(that trends too)

The syntax highlighter here sucks, so you may want to read the code here: http://pastie.org/8494639

You can drop the code into a ruby terminal and it will output a string that you can copy/paste into google charts playground here: https://code.google.com/apis/ajax/playground/?type=visualization#line_chart

# In order to generate a semi-realistic looking graph behavior
# we use a sine function to generate periodic behavior(ups and downs).  In order to avoid
# a graph that is too regular, we introduce randomness at two levels:
# The delta between steps across the x-axis is random, but within a range(deltavariance)
# The wavelength of the sine function is varied by randomly incrementing the index we pass
# to the sine function(sine_index)

# CONFIGURATION VARIABLES
yvalue = 1 # start value
range = 100 # y-range
deltavariance = 10 # allowable variance between changes
sine_index, wavelength = 0, 0.33 #index into our sine function that determines whether we change direction or not
i, maxi = 0, 100 # our counter and its maximum
data = {sine_index => yvalue} # seed our data structure with its first value
trend = :positive # :negative, :none # do we want the graph to trend upwards, downwards or neither
periodmin, periodmax = 0, 0 # vars to enforce trending
direction = 1 # start in a positive direction, -1 for negative

# DO NOT EDIT BELOW THIS LINE
while(i < maxi)

  olddirection = direction
  direction = Math.sin(sine_index).to_f
  direction = direction < 0 ? direction.floor : direction.ceil

  delta = rand(deltavariance) 
  yvalue += delta * direction

  if trend == :positive 
    yvalue = periodmin if yvalue < periodmin
    periodmin = yvalue if olddirection < direction
  elsif trend == :negative
    yvalue = periodmax if yvalue > periodmax
    periodmax = yvalue if olddirection > direction

  end

  data[sine_index] = yvalue
  sine_index += Math.sin(rand) # Math.sin(rand) will give random numbers from -1..1
  i += 1
end

code = <<-CODE
function drawVisualization() {
  // Create and populate the data table.
  var data = google.visualization.arrayToDataTable([
    ['x', 'Cats'],
    DATASTR
  ]);

  // Create and draw the visualization.
  new google.visualization.LineChart(document.getElementById('visualization')).
      draw(data, {curveType: "function",
                  width: 500, height: 400,
                  vAxis: {maxValue: 10}}
          );
}
CODE

datastr = data.collect{|k,v|  "[#{k},#{v}]"}.join(",")
code = code.gsub('DATASTR', datastr)
puts code