code: function partial( sigma ) {
  	var s2 = pow( sigma, 2 );
  	/**
  	* FUNCTION: pdf( x )
  	*	Evaluates the probability density function (PDF) for a Rayleigh distribution.
  	*
  	* @private
  	* @param {Number} x - input value
  	* @returns {Number} evaluated PDF
  	*/
  	return function pdf( x ) {
  		if ( x < 0 ) {
  			return 0;
  		}
  		return (1/s2) * x * exp( -pow( x, 2 ) / ( 2 * s2 ) );
  	};
  }
docs: PARTIAL // 
  FUNCTION: partial( sigma )
  Partially applies scale parameter `sigma` and returns a function for evaluating the probability density function (PDF) for a Rayleigh distribution.
  
  @param {Number} sigma - scale parameter
  @returns {Function} PDF