code: def poincare_ball_exp(c, x, v):
      r"""
      The exponential map of ``v`` at ``x`` on the Poincaré ball with curvature ``-c``:
      :math:`\exp_{\mathbf{x}}^c(\mathbf{v})`.
  
      See Section 2 of [1] for more details.
  
      [1] O.-E. Ganea, G. Bécigneul, and T. Hofmann, “Hyperbolic Neural Networks,” `arXiv:1805.09112 <http://arxiv.org/abs/1805.09112>`_, Jun. 2018.
  
      Args:
          c (tensorflow Tensor-like): the curvature of the hyperbolic space(s). Must be able to be
              broadcast to ``x`` and ``v``.
  
          x (tensorflow Tensor-like, optional): a tensor containing vectors in hyperbolic space
              representing the base points for the exponential map, where each vector is an element of
              the last axis (for example, if ``x`` has shape ``(2, 3, 4)``, it represents ``2 * 3 =
              6`` hyperbolic vectors, each of length ``4``). Must be able to be broadcast to ``v``. An
              explicit ``x = None`` is equivalent to ``x`` being all zeros, but uses a more efficient
              form of :math:`\exp_{\mathbf{0}}^c(\mathbf{v})`.
  
          v (tensorflow Tensor-like): a tensor containing vectors in Euclidean space representing the
              tangent vectors for the exponential map, where each vector is an element of the last
              axis similar to ``x``. Must be able to be broadcast to ``x``.
      """
  
      v_norm2 = tf.reduce_sum(v * v, axis=-1, keepdims=True)
      c_v_norm = tf.sqrt(c * v_norm2)
  
      if x is None:
          coeff = _tanh(c_v_norm) / c_v_norm
          return _project(c, coeff * v)
  
      x_norm2 = tf.reduce_sum(x * x, axis=-1, keepdims=True)
      inner = c_v_norm / (1 - c * x_norm2)
      coeff = _tanh(inner) / c_v_norm
      return poincare_ball_mobius_add(c, x, coeff * v)
  
file_path: stellargraph/stellargraph/utils/hyperbolic.py
imports: import tensorflow
  import numpy
label_desc: Use image node_id 5 for calling a global function with example usage: poincare_ball_exp(c, x, v) and returns: poincare_ball_mobius_add, _project