χ²pdf( is the χ² probability density function.
Since the χ² distribution is continuous, the value of χ²pdf( doesn't represent an actual probability — in fact, one of the only uses for this command is to draw a graph of the χ² curve. You could also use it for various calculus purposes, such as finding inflection points.
The command takes two arguments: the value at which to evaluate the p.d.f., and df, the number of 'degrees of freedom'.
The value of χ²pdf( is given by(1)