function logpdf( x, mu, s ) {
	var z;
	if (
		isnan( x ) ||
		isnan( mu ) ||
		isnan( s ) ||
		s < 0.0
	) {
		return NaN;
	}
	if ( s === 0.0 ) {
		return ( x === mu ) ? PINF : NINF;
	}
	if (
		x < mu - s ||
		x > mu + s
	) {
		return NINF;
	}
	z = ( x - mu ) / s;
	return ln( 1.0 + cospi( z ) ) - ln( 2.0 * s );
}
Evaluates the logarithm of the probability density function (PDF) for a raised cosine distribution with location parameter `mu` and scale parameter `s` at a value `x`.

@param {number} x - input value
@param {number} mu - location parameter
@param {NonNegativeNumber} s - scale parameter
@returns {number} evaluated logPDF

@example
var y = logpdf( 2.0, 0.0, 3.0 );
// returns ~-2.485

@example
var y = logpdf( 1.5, 4.0, 4.0 );
// returns ~-2.562

@example
var y = logpdf( NaN, 0.0, 1.0 );
// returns NaN

@example
var y = logpdf( 0.0, NaN, 1.0 );
// returns NaN

@example
var y = logpdf( 0.0, 0.0, NaN );
// returns NaN

@example
// Negative scale parameter:
var y = logpdf( 2.0, 0.0, -1.0 );
// returns NaN

@example
var y = logpdf( 2.0, 8.0, 0.0 );
// returns -Infinity

@example
var y = logpdf( 8.0, 8.0, 0.0 );
// returns Infinity