function j1( x ) {
	return addon( x );
}
Computes the Bessel function of the first kind of order one.

@private
@param {number} x - input value
@returns {number} evaluated Bessel function

@example
var v = j1( 0.0 );
// returns 0.0

@example
var v = j1( 1.0 );
// returns ~0.440

@example
var v = j1( Infinity );
// returns 0.0

@example
var v = j1( -Infinity );
// returns 0.0

@example
var v = j1( NaN );
// returns NaN