Returns the fraction of zeros in value.

If value is empty, the result is nan.

This is useful in summaries to measure and report sparsity. For example,

    z = tf.nn.relu(...)
    summ = tf.compat.v1.summary.scalar('sparsity', tf.nn.zero_fraction(z))

value A tensor of numeric type.
name A name for the operation (optional).

The fraction of zeros in value, with type float32.