Constants to control the `elbo` calculation.

`analytic_kl` uses the analytic KL divergence between the
variational distribution(s) and the prior(s).

`analytic_entropy` uses the analytic entropy of the variational
distribution(s).

`sample` uses the sample KL or the sample entropy is the joint is provided.

See `elbo` for what is used with `default`.
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#### `tf.contrib.bayesflow.variational_inference.ELBOForms.check_form(form)` {#ELBOForms.check_form}




