code: def custom_gradient(*grad_funcs):
      """Decorate a function to define its custom gradient(s).
  
      This is a placeholder in order to have consistent backend APIs.
      """
  
      def decorator(func):
          return func
  
      return decorator
  
file_path: geomstats/geomstats/_backend/numpy/autodiff.py
imports: from geomstats.exceptions import AutodiffNotImplementedError
label_desc: Use image node_id 7 for calling a global function with example usage: custom_gradient() and returns: decorator, func