code: public SDVariable sizeAt(String name, SDVariable in, int dimension) {
          SDVariable ret = f().sizeAt(in, dimension);
          return updateVariableNameAndReference(ret, name);
      }
docs: Returns a rank 0 (scalar) variable for the size of the specified dimension.
  For example, if X has shape [10,20,30] then sizeAt(X,1)=20. Similarly, sizeAt(X,-1)=30
  
  @param name      Name of the output variable
  @param in        Input variable
  @param dimension Dimension to get size of
  @return Scalar SDVariable for size at specified variable