`HalfNormalDistribution`¶

represents a half-normal distribution with parameter theta.

$ wo 'HalfNormalDistribution[1]'
HalfNormalDistribution[1]

The mean is 1/theta:

$ wo 'Mean[HalfNormalDistribution[a]]'
a^(-1)

The variance is (Pi - 2) / (2 theta^2):

$ wo 'Variance[HalfNormalDistribution[a]]'
(-2 + Pi)/(2*a^2)

The median is Sqrt[Pi] InverseErf[1/2] / theta:

$ wo 'Median[HalfNormalDistribution[a]]'
(Sqrt[Pi]*InverseErf[1/2])/a

HalfNormalDistribution¶