function mode( v ) {
	return addon( v );
}
Evaluates the mode for a Student's t-distribution with degrees of freedom `v`.

@private
@param {number} v - degrees of freedom
@returns {number} mode

@example
var y = mode( 5.0 );
// returns 0.0

@example
var y = mode( 3.0 );
// returns 0.0

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

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