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Michael178
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"CAS.diff(x)" returns "0", incorrectly, even though "CAS.diff(1*x) returns "1", correctly.

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HP Prime calculator

Two different Prime calculators, both an older version and the most recent G2, give an incorrect "0" when "CASdiff(x)" or "CASdiff(1x)" is executed, even though "CASdiff(1*x)" gives the correct answer "1", and "CASdiff(nx)" and CASdiff(n*x)" seem to give the correct answer "n" for every n other than 1. For example, "CASdiff(3x)" returns "3". ("CASdiff(_)" is accessed by pressing the toolbox key, then, with "CAS" selected, "2", "Calculus", next "1", "Differentiate".) Does HP know about this, is there any good reason for it, and are there similar problems for any other arguments of "CASdiff(_)", or any other Prime functions?

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Tim_Wessman
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I assume you are using this in the HOME screen that does not support symbolic differentiation. You have written CAS.diff(x), but i suspect you are actualy using X not x. Case matters for variables.

 

X is a predefined numerical variable, not a symbolic one. Thus it gets replaced by 0, and diff(0) is... 0.

 

 

TW

Although I work for the HP calculator group as a head developer of the HP Prime, the views and opinions I post here are my own.
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Michael178
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I was indeed using CAS.diff() in the HOME screen; when I go thru the access sequence I specified (toolbox> 2>1) in the CAS screen, I get just "diff()", which seems to work, in the CAS screen, the same as "CAS.diff()" does in the HOME screen. (You're correct, I was using "X", not "x" in the HOME screen.) The HOME screen  does support symbolic differentiation; when I execute "CAS.diff(X^2)" in the HOME screen (with "2" as an actual superscript instead of with "^2"; I can't type superscripts on this HP screen) I get "2X", not a number symbol (i.e., digit such as "0", "1", "2", ...), & similarly for all other inputs I've tried to "CAS.diff" except "X". Also, as I said, "3X" as an argument instead of "X" gives "3" instead of "0". If the "X" in "3X" were replaced by "0", "3X" as an argument would also give "0". (One oddity, when I just again tried CAS.diff(1X) I got "1", not "0" as I said in my question that I did; I don't know what caused this change. When I executed "CAS.diff(1X)" [pressed "Enter"] the "1X" was replaced by "1*X" automatically, and "1" returned as an answer. However, "CAS.diff(X)" still gives "0".)

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