code: public SDVariable sub(String varName, double scalar) {
          val result = sameDiff.f().sub(this, scalar);
          return sameDiff.updateVariableNameAndReference(result, varName);
      }
docs: Scalar subtraction: {@code out = this - scalar}<br>
  Output variable has the same shape as the input variable
  
  @param varName Output variable name
  @param scalar  Scalar for operation
  @return Output variable