function factory( x0, gamma ) {
	var gpi;
	if (
		isnan( gamma ) ||
		isnan( x0 ) ||
		gamma <= 0.0
	) {
		return constantFunction( NaN );
	}
	gpi = gamma * PI;
	return pdf;

	/**
	* Evaluates the probability density function (PDF) for a Cauchy distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated PDF
	*
	* @example
	* var y = pdf( 2.3 );
	* // returns <number>
	*/
	function pdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		return 1.0 / ( gpi * (1.0 + pow( (x-x0)/gamma, 2.0 )) );
	}
}
Returns a function for evaluating the probability density function (PDF) for a Cauchy distribution with location parameter `x0` and scale parameter `gamma`.

@param {number} x0 - location parameter
@param {PositiveNumber} gamma - scale parameter
@returns {Function} PDF

@example
var pdf = factory( 4.0, 2.0 );

var y = pdf( 10.0 );
// returns ~0.0159

y = pdf( 3.0 );
// returns ~0.127