Why is exp used in encoder of VAE instead of using the value of standard deviation alone?

There’s one VAE example here: https://towardsdatascience.com/teaching-a-variational-autoencoder-vae-to-draw-mnist-characters-978675c95776 And the source code of encoder: https://gist.github.com/FelixMohr/29e1d5b1f3fd1b6374dfd3b68c2cdbac#file-vae-py The author is using exp (natural exponential) for calculating values of the embedding vector: $z = Mean + Random \times e^{StandardDeviation}$ z = mn + tf.multiply(epsilon, tf.exp(sd)) It’s not related to the code (practical programming), but why using natural exponential instead of:…