function incrmda() {
	var mean;
	var FLG;
	var f0;
	var a0;

	mean = incrmean();
	return accumulator;

	/**
	* If provided a value, the accumulator function returns an updated mean directional accuracy. If not provided a value, the accumulator function returns the current mean directional accuracy.
	*
	* @private
	* @param {number} [f] - forecast value
	* @param {number} [a] - actual value
	* @returns {(number|null)} mean directional accuracy or null
	*/
	function accumulator( f, a ) {
		var sf;
		var sa;
		if ( arguments.length === 0 ) {
			return mean();
		}
		if ( FLG === void 0 ) {
			FLG = true;
			f0 = f;
			a0 = a;
		}
		sf = signum( f-f0 );
		sa = signum( a-a0 );
		f0 = f;
		a0 = a;
		return mean( kroneckerDelta( sf, sa ) );
	}
}
Returns an accumulator function which incrementally computes the mean directional accuracy.

@returns {Function} accumulator function

@example
var accumulator = incrmda();

var m = accumulator();
// returns null

m = accumulator( 2.0, 3.0 );
// returns 1.0

m = accumulator( -5.0, 4.0 );
// returns 0.5

m = accumulator();
// returns 0.5