code: public SDVariable mean(String name, boolean keepDims, int... dimensions){
          return sameDiff.mean(name, this, keepDims, dimensions);
      }
docs: Mean (average) array reduction operation, optionally along specified dimensions<br>
  Note that if keepDims = true, the output variable has the same rank as the input variable,
  with the reduced dimensions having size 1. This can be useful for later broadcast operations (such as subtracting
  the mean along a dimension).<br>
  Example: if input has shape [a,b,c] and dimensions=[1] then output has shape:
  keepDims = true: [a,1,c]<br>
  keepDims = false: [a,c]
  
  @param name       Output variable name
  @param keepDims   If true: keep the dimensions that are reduced on (as size 1). False: remove the reduction dimensions
  @param dimensions Dimensions to reduce over. If dimensions are not specified, full array reduction is performed
  @return Reduced array of rank (input rank - num dimensions)