code: public SDVariable pad(SDVariable input, SDVariable padding, double constant){
          return pad(null, input, padding, Pad.Mode.CONSTANT, constant);
      }
docs: Perform padding on the given array, where padded values are the specified constant.<br>
  Example:<br>
  Input array:<br>
  [1, 2]<br>
  [3, 4]<br>
  Padding array:<br>
  [2, 0]<br>
  [1, 1]<br>
  Contant = 0<br>
  Result:<br>
  [0, 0, 0, 0]<br>
  [0, 0, 0, 0]<br>
  [0, 1, 2, 0]<br>
  [0, 3, 4, 0]<br>
  <br>
  
  
  @param input    Input array to pad
  @param padding  Padding array
  @param constant Constant to use for padded values
  @return Padded array