function igammaTemmeLarge( a, x ) {
	var result;
	var sigma;
	var phi;
	var y;
	var z;

	sigma = ( x-a ) / a;
	phi = -log1pmx( sigma );
	y = a * phi;
	z = sqrt( 2.0 * phi );
	if ( x < a ) {
		z = -z;
	}
	workspace[ 0 ] = polyvalC0( z );
	workspace[ 1 ] = polyvalC1( z );
	workspace[ 2 ] = polyvalC2( z );
	workspace[ 3 ] = polyvalC3( z );
	workspace[ 4 ] = polyvalC4( z );
	workspace[ 5 ] = polyvalC5( z );
	workspace[ 6 ] = polyvalC6( z );
	workspace[ 7 ] = polyvalC7( z );
	workspace[ 8 ] = polyvalC8( z );
	workspace[ 9 ] = -0.00059676129019274625;
	result = evalpoly( workspace, 1.0/a );
	result *= exp( -y ) / sqrt( TWO_PI * a );
	if ( x < a ) {
		result = -result;
	}
	result += erfc( sqrt(y) ) / 2.0;
	return result;
}
Asymptotic expansions of the incomplete gamma functions when `a` is large and `x ~ a` (IEEE double precision or 10^-17).

@private
@param {number} a - function parameter
@param {number} x - function parameter
@returns {number} value of asymptotic expansion