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When we integrate a function:

$ \int^b_a {2\over x^2} dx$

The expression to be integrated (is this case $ {2\over x^2} $) is referred to as the integrand.

When we differentiate a function:

$ {d \over dx } {2 \over x^2}$

Is there a word to describe the expression to to be differentiated? For instance, if I wanted to say "In the above equation, two over x squared is the --------", what would I fill in the blank?

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    $\begingroup$ Given function?? $\endgroup$
    – imranfat
    Commented Jan 29, 2014 at 20:51
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    $\begingroup$ Clearly, it's the differentiand. Though, strangely, Google doesn't recognize this term. $\endgroup$ Commented Jan 29, 2014 at 20:54
  • $\begingroup$ Follow-up question: is there any reason why you would need such a term? I don't think "integrand" is used beyond calculus either. $\endgroup$
    – Lost
    Commented Jan 29, 2014 at 22:45
  • $\begingroup$ @Lost I'm writing a program where I have a higher-order function that accepts another function as input and differentiates it, and I'm looking for something to name the argument. $\endgroup$ Commented Jan 29, 2014 at 23:10
  • $\begingroup$ @ValekHalfHeart Fair enough. As others have said, there doesn't seem to be a commonly used term, so anything is fair game. $\endgroup$
    – Lost
    Commented Jan 29, 2014 at 23:13

3 Answers 3

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Call it the differentiand and everyone will know what you mean. It's unambiguous, but certainly not in regular use.

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  • $\begingroup$ "Differentiand" is horrible! If you need to invent a word, "differand" is surely better. $\endgroup$
    – TonyK
    Commented Jan 29, 2014 at 21:17
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    $\begingroup$ I'm just following the horrible rules of Latin. $\endgroup$ Commented Jan 29, 2014 at 21:34
  • $\begingroup$ Yes OK, but why? $\endgroup$
    – TonyK
    Commented Jan 29, 2014 at 21:35
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    $\begingroup$ There is no really good answer to "why". First: symmetry is something mathematicians love. Why name the intgrand one way but the differentiand another? Second: Latin was the language of Leibniz' and Newton's papers which formalized infinitessimal calculus. If we were inventing a new concept I might use a new language, but since we're finding a name for something well known in the 17th century, using the language of its inventors seems apropos. $\endgroup$ Commented Jan 30, 2014 at 0:20
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I'd just call it "the expression being differentiated."

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We say "operand" for thing being operated on. So if we differentiate, we should say, "differetiand." although the shortening by Tony K might be an improvement on this messy word.

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