def expmap_to_quaternion(e):
    """
    Convert axis-angle rotations (aka exponential maps) to quaternions.
    Stable formula from "Practical Parameterization of Rotations Using the Exponential Map".
    Expects a tensor of shape (*, 3), where * denotes any number of dimensions.
    Returns a tensor of shape (*, 4).
    """
    assert e.shape[-1] == 3

    original_shape = list(e.shape)
    original_shape[-1] = 4
    e = e.reshape(-1, 3)

    theta = np.linalg.norm(e, axis=1).reshape(-1, 1)
    w = np.cos(0.5 * theta).reshape(-1, 1)
    xyz = 0.5 * np.sinc(0.5 * theta / np.pi) * e
    return np.concatenate((w, xyz), axis=1).reshape(original_shape)

    Convert axis-angle rotations (aka exponential maps) to quaternions.
    Stable formula from "Practical Parameterization of Rotations Using the Exponential Map".
    Expects a tensor of shape (*, 3), where * denotes any number of dimensions.
    Returns a tensor of shape (*, 4).
    
mGPT/data/humanml/common/quaternion.py