code: public SDVariable[] unstack(String[] names, @NonNull SDVariable value, int axis, int num) {
          SDVariable[] ret = f().unstack(value, axis, num);
          return updateVariableNamesAndReferences(ret, names);
      }
docs: Unstack a variable of rank X into N rank X-1 variables by taking slices along the specified axis.
  If input has shape [a,b,c] then output has shape:
  axis = 0: [b,c]<br>
  axis = 1: [a,c]<br>
  axis = 2: [a,b]<br>
  
  @param names Output variable names. May be null
  @param value Input variable to unstack
  @param axis  Axis to unstack on
  @param num   Number of output variables
  @return Output variables
  @see #stack(String, int, SDVariable...)