Mapping from user input to scores

z_score

require 'distribution'
module Z
  extend self
  Z_EPSILON = 10e-16
  Z_MAX = 6.0
  
  def critical_z(p)
    minz = -Z_MAX
    maxz = Z_MAX
    zval = 0.0
    
    return -1 unless (0..1) === (p)
    
    while ((maxz - minz) > Z_EPSILON)
      pval = Distribution::Normal.cdf(zval)
      
      if pval > p
        maxz = zval
      else
        minz = zval
      end
      
      zval = (maxz + minz) * 0.5
    end
    zval
  end
  
  
  def score(p)
    if (0..1) === p
      critical_z(p)
    else
      raise 'Must be between 0 and 1'
    end
  end
end