function logpmf( x ) {
		var out;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( isNonNegativeInteger( x ) ) {
			if ( x > n ) {
				return NINF;
			}
			out = binomcoefln( n, x );
			out += (x * ln( p )) + ((n - x) * log1p( -p ));
			return out;
		}
		return NINF;
	}
Evaluates the natural logarithm of the probability mass function (PMF) for a binomial distribution.

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

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