{ BBAND.TAS - This script computes BOLLINGER BANDS. 
  Bollinger bands are lines which are 'n' standard deviations away 
  from a 'p' day moving average of the close. 
  To change the value of 'n', change 'bband_devs' below. To 
  change the value of 'p', change 'bband_period' below.
}


#output_file 'bband.lst'
bband_period = 20;              { number of days in BBAND period }
bband_devs   = 2;               { number of STD DEVIATIONS about close}
bband_top : array;              { top band }
bband_bot : array;              { bottom band }
stddev    : array;              { good old std dev }
movavg    : array;              { and the moving avg }

{ compute n day sma of close}
movavg = mov(c,bband_period,'S');    

{ and the std dev of close same period}
stddev = std(c,bband_period); 

{ Now, compute the number of standard deviations about the close 
  by default, this is 2
}
stddev = mulby(stddev,bband_devs);       

{ 
  Now add the std deviations to the moving average to get the top 
  Bollinger Band 
}
bband_top = add(movavg,stddev);
{ 
  Now subtract the std deviations from the moving average to get 
  the bottom Bollinger Band 
}
bband_bot = sub(movavg,stddev);

{ Now, the rest is up to you. I have suppied a simple check to see
  if the current close is over the top band or below the bottom band.
  You can use these BBAND arrays to check for the narrowing of the 
  bands, tops or bottoms outside the bands, and bouncing off the 
  bands.
}

if over(c,bband_top) > 0 then
  writeln(ticker,' BBAND upward breakout occurred');
if over(bband_bot,c) > 0 then
  writeln(ticker,' BBAND downward breakout occurred');