function triangular( u ) {
	var absU;
	if ( isnan( u ) ) {
		return NaN;
	}
	absU = abs( u );
	if ( absU > 1.0 ) {
		return 0.0;
	}
	return 1.0 - absU;
}
Computes the triangular kernel for a value.

@private
@param {number} u - input value
@returns {number} kernel value at u

@example
var u = 0.2;
var out = triangular( u );
// returns 0.8