(PECL stats >= 1.0.0)
stats_dens_weibull — Probability density function of the Weibull distribution
$x, float $a, float $b): float
   Returns the probability density at x, where the
   random variable follows the Weibull distribution of which the shape parameter
   is a and the scale parameter is b.
  
xThe value at which the probability density is calculated
aThe shape parameter of the distribution
bThe scale parameter of the distribution
   The probability density at x or false for failure.