function getMax( arr ) {
	var max;
	var i;
	if ( arr.length === 0 ) {
		return null;
	}
	max = arr[ 0 ];
	for ( i = 1; i < arr.length; i++ ) {
		if ( arr[ i ] > max ) {
			max = arr[ i ];
		}
	}
	return max;
}
Computes a maximum value.

@private
@param {NumericArray} arr - input array
@returns {(number|null)} maximum value or null