function logpdf( x, mu, s ) {
	return addon( x, mu, 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`.

@private
@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