# Does 常数 only refer to commonly used, fixed numerical constants like 1 or π or c, or can it refer to e.g. 384810513112?

I got a bit confused talking maths with my iTalki teacher today. We encountered the term:

CC-CEDICT: 常数 (cháng​shù​) a constant (math.)

On one hand, since 常 appears in 常用, 常常, 经常, etc., the 常 in 常数 makes me think that it refers to commonly used, fixed mathematical numbers, like 1 or π or c, as opposed to some random number, like 384810513112. On the other hand, 常数 might be contrasted with 变数 = "variable", in which case 384810513112 would be considered a 常数, since it doesn't 变.

Question: Does 常数 only refer to commonly used, fixed numerical constants like 1 or π or c, or can it refer to e.g. 384810513112?

Baidu Baike seems to suggest 常数 exclusively refers to special numbers, like 1 or π or c. But then, it's not clear to me what a constant like 384810513112 would be called.

• 常数 = constant (math).
– r13
Jan 6, 2023 at 16:21

It depends on the context. Most probably, if you say 常数, you are referring to a number of mathematical or physical significance.

Note that 常量 may also represent significant numbers, like G is commonly referred to as 引力常量。

If you are using 常数, chances are that you need to explicitly define it, in which use I believe using it is okay.

Thus, if you use it independently without constant, people will think it means a significant number. If you have a context, then it is OK to refer to a random number.

Another use case for 常数 is that when you say a formula evaluates to a constant. 一个常数 is often used and it is solely used as the object.

Another interesting perspective is a programmer's, consider the following code snippet.

``````const int N = 100;
``````

In this case, you can say

N 是一个被定义为 100 的常量。

In the dictionary, https://www.zdic.net/hans/%E5%B8%B8, 常 has 3 meanings (not including the surname). (1) normal, (2) frequent (frequently), (3) invariable.

In Mathematics, 常数 is the opposite of 变数. For example, y = kx is a linear function, where the slope k is a constant and x is a variable. There are other concepts in Mathematics, such as 系数 and 参数. 系数 is more like a 常数, and 参数 is more like a 变数.

In science, such as physics and chemistry, 常数 is often called 常量, which has a specific value from the experiments and research.

In computer programming, 常量 and 变量 are named storage units. 常量 (constant) is assigned a value at the beginning of the program, and would not change until the end of the program.

• 光速 ，299,792,458 m/s，是一個 物理常數.

• π[pai], 圓周率, 是一個數學常數（約等於3.141592654).

Note: 常数 usually comes with a unit to give the meaning of the numerical value. For example, 光速 = 299,792,458 m/s, in which, 299,792,458 is the numerical value, and m/s is the unit of the speed of light.

• Is that really how the word is derived? I think 常 here comes from 常量 and similar words, i.e. the "constant; fixed" meaning of 常, not 常用. Jan 14, 2023 at 9:12
• @OlleLinge 常数=恒/常量=a constant (a number having an unchanging value). zdic.net/hans/%E5%B8%B8%E9%87%8F, zdic.net/hans/%E5%B8%B8%E6%95%B8, dict.cn/constant
– r13
Jan 14, 2023 at 12:57
• I know what the words mean, my comment was about the derivation you presented in your reply : "常数 = 常用數值". Jan 16, 2023 at 18:10
• @OlleLinge In the US, we use g = 9.81 m/sec^2 as the constant for gravity, however, 9.81 is a "commonly used value" (常用數值) rather than an "absolute value" (絕對數值/固值). 常用數值 is a selectively assigned value; 絕對數值 is a scientifically determined value. Hope you see the differences.
– r13
Jan 16, 2023 at 19:03
• Yes, I do! I've always thought of 常 as meaning "not changing" rather than "common/often" in the word 常数, hence my question. Jan 16, 2023 at 19:43