function tricube( u ) {
	var absU;

	if ( isnan( u ) ) {
		return NaN;
	}
	absU = abs( u );
	if ( absU > 1.0 ) {
		return 0.0;
	}
	return LEADING_TERM * pow( 1.0 - pow( absU, 3.0 ), 3.0 );
}
Computes the tricube kernel for a value.

@private
@param {number} u - value for which we wish to calculate the tricube kernel
@returns {number} the value for the kernel at u

@example
var u = 5;
out = tricube(u);
// returns 0.0