# Why do we use the word “regime” in math/science/engineering instead of “region”?

For example, I would hear people say in the "regime" of x>3? Does it have a different meaning/origin to the "region" of x>3? To me, "region" sounds like the more proper term.

Edit: I have heard this usage in a few context in physics, electrical engineering, and machine learning. It usually involves the professors pointing at a 2D graph and articulating about the behavior of a system/model/function in these "regimes".

• I have never heard that terminology. – MathematicsStudent1122 Dec 11 '17 at 22:13
• Perhaps that's how you call "domain" in your language. Your example would be a misusage of the terminology, though: if $f:X\to Y$ is a function, domain of $f$ is the term that indicates the set $X$. If this is the case, the appropriate way to state the sentence would be "$f$ has domain $\{x\in\Bbb R\,:\, x>3\}$" or something along those lines. – user228113 Dec 11 '17 at 22:16
• Regime: the conditions under which a scientific or industrial process occurs – Flame Trap Dec 11 '17 at 22:49
• Flame Trap is correct. It also may be used in other circumstances, depending on the author, but "regime" is occasionally used for the domain of variables that model physical processes. Often there is a connotation that the boundaries of the regime are not well-defined. (Physical measurements of continuous quantities are limited in accuracy both by measuring capability and by their definition.) I think this is a major reason "regime" is used instead of "region". – Paul Sinclair Dec 12 '17 at 3:48
• maybe you are on to something @PaulSinclair – godlamp Dec 13 '17 at 20:39