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I want to write in a math article that one parameter is going up when other is falling. These parameters are linked. What is a formal way of writing it? "Parameter A is rise with the fall of parameter B"?

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Going from a hunch, I would suggest "inversely proportional." If you are writing this article for a school or class you can probably get a great answer from a local math teacher or professor.

Edit: Okay, I guess I should have known that there was a technical definition of "inversely proportional." Wikipedia has a quick description, as do the comments here.

For example, the time taken for a journey is inversely proportional to the speed of travel; the time needed to dig a hole is (approximately) inversely proportional to the number of people digging.

So, inversely proportional is one type of rising with the fall of something else. A more generic term will be more appropriate.

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    No: _inversely proportional_ in mathematics usually means precisely that the two parameters multiply to a constant (e.g., as `x` rises `y` goes down because `y=2/x`).2011-04-05
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    @msh210 What you are saying, and MrHen's answer, don't conflict in the least.2011-04-05
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    Thank you. I would rather have to meet with my English teacher ... :). What about: Parameter A rises with the fall of parameter B. Is it OK or I should try to come up with something else ?2011-04-05
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    @Billare Actually, it's not entirely clear: The OP's question doesn't specify the rate at which one rises and the other falls. @msh210 is correct in that inverse proportionality applies only to a constant rate. It is simpler (and possibly more accurate) to say while one increases, the other will decrease.2011-04-05
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    @Billare: the mathematical relationship given by “inversely proportional” is much more specific than “one rises as the other falls”. For instance, suppose I’m travelling from London to Paris in a straight line. Then the distance from London rises as the distance from Paris falls — but these are *not* inversely proportional. This example is a relationship of the form *y = c – x* (where *c* is constant); inversely proportional means just relationships of the form *y = c/x*.2011-04-05
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    @PLL I neglected to see the word "precisely" in msh2010's answer, having just read it over. I had realized what you were saying before, but still thought it wrong to say "no" or "wrong"; _inversely proportional_ **could** very well be the relationship the OP is seeking, though I agree it is not the most general term one could use.2011-04-05
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    @msh; @pll: I edited with a correction and a bit more information. Apologies for the mistake and confusion.2011-04-05
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    @darqer: I personally prefer [@HaL's answer](http://english.stackexchange.com/questions/19607/how-to-say-that-something-rises-with-the-fall-of-something-else/19611#19611).2011-04-05
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    What about *inversely related*?2011-04-05
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Since it's math, you can use increase and decrease:

Parameter A will increase as Parameter B decreases.

Using the conjunction as links the two parameters correlatively.

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Perhaps you are looking for "negative correlation"

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"decreases monotonically with" if you are being technical.

That means A always goes up as B goes down (there are no inflections) - but you aren't saying anything about the relationship.

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If the increasing parameter is a function of the decreasing one, then you just call it a decreasing function of it. (The reason for this name will be clear when you graph the increasing parameter relative to the decreasing one on a pair of axes.)

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A and B are 'Inversely Proportionate'
Or A is inversely proportionate to B
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    @MrHen [suggested this already](http://english.stackexchange.com/questions/19607/how-to-say-that-something-rises-with-the-fall-of-something-else/19609#19609); as comments/edits on his answer show, it’s not exactly correct as an answer to the question, although it might fit the OP’s specific circumstances.2011-04-05
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As one more possibility: "varies inversely".