You can put safeguards in place with external variables, but that would get messy very quickly.

可以利用外部变量采取安全措施，但这会很快引起混乱。

youdao

For controlling the greenhouse environment the first step is to set up a mathematical model which describes the relationship between the external variables and the plant environment.

实行温室控制的首要步骤是建立一个合理的数学模型，用该模型来描述温室外部变量和作物生长环境的关系。

youdao

Chapter 4 covers functions and program structure - external variables, scope rules, multiple source files, and so on - and also touches on the preprocessor.

第4章介绍函数和程序结构—外部变量、作用域规则和多个源文件等，并涉及到预处理器。

youdao

So this isn't the most useful form that we can have, but what we'll see shortly is that from this, we can then derive further criteria for essentially any set of variables or any set of external constraints, like constant temperature or pressure or volume and so forth that we might set.

所以这不是我们所能得到的最有用的形式，但是我们会很快看到，我们能够进一步推导出包含任意变量,或者任意约束的自发过程判断标准，比如说恒定的温度，压强,体积或者其他我们能够给出的约束。

麻省理工公开课 - 热力学与动力学课程节选