function logcdf( x, alpha, beta ) {
	if (
		isnan( x ) ||
		isnan( alpha ) ||
		isnan( beta ) ||
		alpha <= 0.0 ||
		beta <= 0.0
	) {
		return NaN;
	}
	if ( x < beta ) {
		return NINF;
	}
	return log1p( -pow( beta / x, alpha ) );
}
Evaluates the cumulative distribution function (CDF) for a Pareto (Type I) distribution with shape parameter `alpha` and scale parameter `beta` at a value `x`.

@param {number} x - input value
@param {PositiveNumber} alpha - shape parameter
@param {PositiveNumber} beta - scale parameter
@returns {number} evaluated logCDF

@example
var y = logcdf( 2.0, 1.0, 1.0 );
// returns ~-0.693

@example
var y = logcdf( 5.0, 2.0, 4.0 );
// returns ~-1.022

@example
var y = logcdf( 4.0, 2.0, 2.0 );
// returns ~-0.288

@example
var y = logcdf( 1.9, 2.0, 2.0 );
// returns -Infinity

@example
var y = logcdf( +Infinity, 4.0, 2.0 );
// returns 0.0

@example
var y = logcdf( 2.0, -1.0, 0.5 );
// returns NaN

@example
var y = logcdf( 2.0, 0.5, -1.0 );
// returns NaN

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

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

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