function quantile( p, x0, gamma ) {
	if (
		isnan( x0 ) ||
		isnan( gamma ) ||
		gamma <= 0.0 ||
		isnan( p ) ||
		p < 0.0 ||
		p > 1.0
	) {
		return NaN;
	}
	return x0 + ( gamma * tan( PI*( p-0.5 ) ) );
}
Evaluates the quantile function for a Cauchy distribution with location parameter `x0` and scale parameter `gamma` at a probability `p`.

@param {Probability} p - input value
@param {number} x0 - location parameter
@param {PositiveNumber} gamma - scale parameter
@returns {number} evaluated quantile function

@example
var y = quantile( 0.3, 2.0, 2.0 );
// returns ~0.547

@example
var y = quantile( 0.8, 10, 2.0 );
// returns ~12.753

@example
var y = quantile( 0.1, 10.0, 2.0 );
// returns ~3.845

@example
var y = quantile( 1.1, 0.0, 1.0 );
// returns NaN

@example
var y = quantile( -0.2, 0.0, 1.0 );
// returns NaN

@example
var y = quantile( NaN, 0.0, 1.0 );
// returns NaN

@example
var y = quantile( 0.0, NaN, 1.0 );
// returns NaN

@example
var y = quantile( 0.0, 0.0, NaN );
// returns NaN

@example
// Negative scale parameter:
var y = quantile( 0.5, 0.0, -1.0 );
// returns NaN