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HP Forum Archive 21

 HP Prime - Defining a functionMessage #1 Posted by bluesun08 on 22 Oct 2013, 7:13 a.m. How can i define a function for example f(x) = x^2 +8x +4 in den Home-Screen, then calculate f(1), f(2). Then i want to build the derivate of f(x) in CAS. Then i want go plot the graph of f(x) and the derivate f'(x). How can i do this things?

 Re: HP Prime - Defining a functionMessage #2 Posted by Gilles Carpentier on 22 Oct 2013, 5:57 p.m.,in response to message #1 by bluesun08 I do this like this : ```To define f : CAS then f(x):=x˛+8*x+4 To calculate f(1), f(2) . CAS or HOME, and just f(1) or f(2) To built the derivative, CAS, then g:=f' To plot APPS FUNCT F1 f(X) // be carefull about X and not x F2 g(X) Plot Not that : F2 f'(X) doesn't work Perhaps there are other ways ... ``` Edited: 22 Oct 2013, 5:59 p.m.

 Re: HP Prime - Defining a functionMessage #3 Posted by Han on 22 Oct 2013, 10:26 p.m.,in response to message #2 by Gilles Carpentier Quote: I do this like this : ```To define f : CAS then f(x):=x˛+8*x+4 To calculate f(1), f(2) . CAS or HOME, and just f(1) or f(2) To built the derivative, CAS, then g:=f' To plot APPS FUNCT F1 f(X) // be carefull about X and not x F2 g(X) Plot Not that : F2 f'(X) doesn't work Perhaps there are other ways ... ``` ```F1:=f('X'); // need ' ' when using global, built-in, non-CAS variables F2:=f'; // more direct; auto-converts x to X F2:=f'('X'); // more explicit ``` Edited: 22 Oct 2013, 10:28 p.m.

 Re: HP Prime - Defining a functionMessage #4 Posted by Gilles Carpentier on 23 Oct 2013, 4:09 a.m.,in response to message #3 by Han Thank's ! ```F1:=f F2:=f' ``` works fine ;) Edited: 23 Oct 2013, 4:10 a.m.

 Re: HP Prime - Defining a functionMessage #5 Posted by bluesun08 on 23 Oct 2013, 2:13 p.m.,in response to message #4 by Gilles Carpentier Many thanks for your replays. The following things are bad: 1. There is no „:=“ key similary to TI NSPIRE. 2. In CAS the function-letter will be automatically lower case (f) and in HOME screen and in APPS FUNC the function letter will be automatically upper case (F) so that i have another keystroke (Shift) for lower case (f) 3. The small x and the big X in CAS/APPS FUNC are confusing. Questions: 1. How can i reach the ' in the derivate? 2. What is the logic behind the lower case/upper case X/x F/f?

 Re: HP Prime - Defining a functionMessage #6 Posted by Han on 23 Oct 2013, 2:43 p.m.,in response to message #5 by bluesun08 Quote: Many thanks for your replays. The following things are bad: 1. There is no „:=“ key similary to TI NSPIRE. 2. In CAS the function-letter will be automatically lower case (f) and in HOME screen and in APPS FUNC the function letter will be automatically upper case (F) so that i have another keystroke (Shift) for lower case (f) 3. The small x and the big X in CAS/APPS FUNC are confusing. Questions: 1. How can i reach the ' in the derivate? 2. What is the logic behind the lower case/upper case X/x F/f? 1. := can be obtained typing each character using [Alpha][-][Shift][.] 2. Single, capital letters are global, real-valued, system variables; they cannot be deleted. CAS operates with the idea that everything that is not defined is considered symbolic. And if a variable is defined, then its value will always be substituted in first. So for example, if we store 1.25 into 'x', then 1+x is interpreted as 1.25. On the other hand, if 'x' is purged, then 1+x is interpreted as a formula 1+x. 3. Yes, it is. In fact, I would go as far as saying how variables (global, local, within apps, etc) could use an overhaul. 4. [Shift][( )][Backspace] (just get double ' and delete one of them) 5. I am sure there is some "logic" but any time I make an attempt to explain (even to myself) what I think is behind upper vs lower case, I end up finding too many exceptions. I think a large number of problems that arise are the result of a design choice: merging xcas with an HP38GII. The idea itself is fine; but each of those systems has ways of handling variables, command-line input, etc. that are often conflicting at times. Over time, this should be ironed out... Edited: 23 Oct 2013, 2:43 p.m. Go back to the main exhibit hall