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If you have a 2-variable function f(x,y) you can compute its partial derivatives f_x(x,y) and f_y(x,y), but also the mixed partial derivatives f_{xy}(x,y) and f_{yx}(x,y). How do you read these symbols?

closed as off-topic by Edwin Ashworth, Rob_Ster, user067531, AndyT, KarlG Feb 15 '18 at 17:29

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  • If the "_{x,y}" could alternatively be written as a subscript, it would make sense to me to say it "sub x y". But I'm just guessing. – Greg Lee Feb 13 '18 at 23:51
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    This question belongs on another site in the Stack Exchange network_MathematicsSE – Edwin Ashworth Feb 13 '18 at 23:53
  • @Edwin Ashworth : I'm not sure. Math-stackexchange deals with questions about mathematics (I mean problems/exercises/topics). This is not a question about mathematics. I just want to know how read the symbol. – John N. Feb 14 '18 at 0:00
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    The question is likely to be closed here, but it's 'f sub x y of x and y' and 'f sub y x of x and y'. Subscripts are 'sub', functions are 'of', commas are 'and'. – jimm101 Feb 14 '18 at 0:00
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    I agree with the comment by @jimm101 as shorthand for someone who knows that subscripts correspond to differentiation. More precise phrases are "the derivative with respect to x of the function f of x and y and "the second derivative with respect to x and y of the function f of x and y." One could specify "partial derivative," but that's redundant because it's clear that f is a function of multiple variables. – Chemomechanics Feb 14 '18 at 1:47
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This reference might be helpful. Wikipedia total derivative

As your questions suggests, when speaking it isn’t easy to be clear. The written symbols contain information that take more time and effort to express verbally. The word “derivative” could mean total or partial derivative.

I recommend saying “partial derivative of f with respect to x.” Many words but unambiguous.

  • Your question is answer – Zbigniew Sep 11 at 9:39

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