greeks.js
function _putDelta(s, k, t, v, r)
{
  var delta = _callDelta(s, k, t, v, r) - 1;
  return (delta == -1 && k == s) ? 0 : delta;
}
function _putDelta(s, k, t, v, r)
{
  var delta = _callDelta(s, k, t, v, r) - 1;
  return (delta == -1 && k == s) ? 0 : delta;
}
function _putDelta ( s , k , t , v , r ) { var delta = _callDelta ( s , k , t , v , r ) - 1 ; return ( delta == - 1 && k == s ) ? 0 : delta ; }
Calculates the delta of a put option.

@private
@param {Number} s Current price of the underlying
@param {Number} k Strike price
@param {Number} t Time to experiation in years
@param {Number} v Volatility as a decimal
@param {Number} r Anual risk-free interest rate as a decimal
@returns {Number} The delta of the put option
Calculates the delta of a put option .