def METHOD_NAME(S, func, iVal, Val, iConstant, Constant, epsilon=1e-3):
    S.update({iVal: Val, iConstant: Constant})
    val1 = func()
    S.update({iVal: Val + epsilon, iConstant: Constant})
    val2 = func()
    S.update({iVal: Val, iConstant: Constant})
    return (val2 - val1) / epsilon