function quantile( p, d1, d2 ) {
	var xs;
	if (
		isnan( p ) ||
		isnan( d1 ) ||
		isnan( d2 ) ||
		d1 <= 0.0 ||
		d2 <= 0.0 ||
		p < 0.0 ||
		p > 1.0
	) {
		return NaN;
	}
	xs = kernelBetaincinv( d1/2.0, d2/2.0, p, 1.0 - p );
	return d2 * xs[ 0 ] / ( d1 * xs[ 1 ] );
}
Evaluates the quantile function for an F distribution with numerator degrees of freedom `d1` and denominator degrees of freedom `d2` at a probability `p`.

@param {Probability} p - input value
@param {PositiveNumber} d1 - numerator degrees of freedom
@param {PositiveNumber} d2 - denominator degrees of freedom
@returns {number} evaluated quantile function

@example
var y = quantile( 0.8, 1.0, 1.0 );
// returns ~9.472

@example
var y = quantile( 0.5, 4.0, 2.0 );
// returns ~1.207

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

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

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

@example
var y = quantile( 0.5, NaN, 1.0 );
// returns NaN

@example
var y = quantile( 0.5, 1.0, NaN );
// returns NaN

@example
var y = quantile( 0.5, -1.0, 1.0 );
// returns NaN

@example
var y = quantile( 0.5, 1.0, -1.0 );
// returns NaN