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HP Prime function APP - Strange limitation ! :o( - dg1969 - 10-04-2013


In home view inside the function app I plot two functions :

F1(X): AREA(sin(X),0,X) and
F2(X): sincard(X)

sincard(x) was defined with the Define shift key command as sincard(X)=sin(X)/X

The plots are OK BUT inside the plot view it is impossible to use the build in "Menu>Fcn>Extremum" or "Slope"....

The same occur with user function previously defined in cas world with for example f(x):=sin(x)*x

What's wrong ?

Thank's for your help and my apologies for my very bad english...


Edited: 4 Oct 2013, 9:52 a.m.

Function ambiguity - Han - 10-04-2013

I think that the app is behaving correctly. (I don't think the HP48-HP49-HP50G is able to do symbolic manipulations with "program" functions either, for that matter.) Use an explicit function in F2 instead.

Depending on where a "function" is created, it seems to be interpreted differently.

Using DEFINE to create MYFUNC(X), MYFUNC is treated similar to regular non-CAS command, which is quite different from a function created using the CAS screen via:


In this case, FUNC is considered as a function (DOM_FUNC) as well as a CAS program. One cannot use MYFUNC from the CAS to do symbolic calculations such as MYFUNC(a). (This bit is not really an issue -- for me anyway -- as I am sure that it is part of the "CAS vs non-CAS" design.) And all calculations with MYFUNC return non-exact values, again as if MYFUNC were a non-CAS function, as opposed to FUNC which is a CAS function.

Strangely, if we define (in CAS mode):


then f is a symbolic (DOM_SYMBOLIC) and not a function. It is considered a "program" in that it returns program(X,0,X^2-5). However, it does not show up in the program list, and does not evaluate properly. In the CAS screen, typing f(1) produces an "Error:Invalid Input"

On the other hand, symbolic functions such as FUNC (explained above) theoretically _should_ work since the calc is able to properly handle CAS-created functions. However, I am unable to get the tangent line feature to work even with CAS-created functions (perhaps again because CAS-created functions are actually still programs).

Now, since f(X) (as defined above) shows up as a symbolic type, I was thinking perhaps this case should work -- except it doesn't either. In fact, the plot shows up as undefined (even using CAS.f(X) in Symbolic View). One-letter functions seem to be treated differently.

Edited: 4 Oct 2013, 11:48 a.m.

Re: Function ambiguity - dg1969 - 10-04-2013

Thank's for your answer but I'am not sure to understand... I don't want to make symbolic computation I just want numerical approximation in the plot view... root, extremum or slope...

For basic use with my HP50G I can define a user function with a program. For example I can create a var "MYFUNCT" that contains the following :

<< -> x << x 2 ^ 2 - >> >>

Then I can plot MYFUNCT(X) and the build in FCN>SLOPE or EXTREMUM work just fine...

I'd like to do the same with these PRIME...

Edited: 4 Oct 2013, 12:13 p.m.