#! /usr/bin/gawk -f
# Last edited on 2009-12-04 03:05:24 by stolfi

# GAWK library meant to be included in other GAWk programs with "-f".
# Defines some functions that are part of the WP growth model.

function window_factor(tc,b,e,wb)
{
  # Basically 1 between {b} and {e} inclusive, 0 outside;
  # but smoothed over a range of {± wb} days.
  if (tc < b - wb)
    { return 0; }
  else if (tc <= b + wb)
    { return sigmoid((tc - b + 0.0)/(wb + 1.0)); }
  else if (tc < e - wb)
    { return 1; }
  else if (tc <= e + wb)
    { return sigmoid((e - tc + 0.0)/(wb + 1.0)); }
  else 
    { return 0; }
}

function sigmoid(x)
{ 
  # A sigmoid function that goes from 0 to 1 as {x} goes from -1 to +1.
  if (x <= -1.0)
    { return 0; }
  else if (x < +1.0)
    { x = sin(0.5*pi*x);
      x = sin(0.5*pi*x);
      return 0.5*(x + 1);
    }
  else 
    { return 0; }
}