function mode( c ) {
	if (
		isnan( c ) ||
		c <= 0.0
	) {
		return NaN;
	}
	return 0.0;
}
Returns the mode of a Bradford distribution.

@param {PositiveNumber} c - shape parameter
@returns {NonNegativeNumber} mode

@example
var v = mode( 0.1 );
// returns 0.0

@example
var v = mode( 0.5 );
// returns 0.0

@example
var v = mode( 10.0 );
// returns 0.0

@example
var v = mode( 0.0 );
// returns NaN

@example
var v = mode( -1.0 );
// returns NaN

@example
var v = mode( NaN );
// returns NaN