// filtre Bell
function result = bellFilter(value)

  if (Value < 0.0) 
    value = -value;
  end;

  if (value < 0.5) 
     result = 0.75 - sqr(value);
  elseif (value < 1.5)
     value = value - 1.5;
     result = 0.5 * sqr(value);
  else
     result = 0.0;
  end;

endfunction;