code: public SDVariable mean(String name, SDVariable x, int... dimension) {
          return mean(name, x, false, dimension);
      }
docs: Mean (average) array reduction operation, optionally along specified dimensions
  
  @param name      Output variable name
  @param x         Input variable
  @param dimension Dimensions to reduce over. If dimensions are not specified, full array reduction is performed
  @return Reduced array of rank (input rank - num dimensions)