function cdf( x ) {
		var z;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < mu - s ) {
			return 0.0;
		}
		if ( x > mu + s ) {
			return 1.0;
		}
		z = ( x - mu ) / s;
		return ( 1.0 + z + ( sinpi( z ) / PI ) ) / 2.0;
	}
Evaluates the cumulative distribution function (CDF) for a raised cosine distribution.

@private
@param {number} x - input value
@returns {Probability} evaluated CDF

@example
var y = cdf( 2.0 );
// returns <number>