How to clear x



#2

I want to clear x so I can use it as a symbolic variable. I am sure that I have cleared it previously.
How do you clear it, I have even tried x:='x'?

Thank you Michael Carey


#3

type and enter purge(x)


#4

Thank you for your quick reply Michael.

I get a "No such variable x."

I am using lower case x and in the CAS view, I tried all the obvious other combinations.

Thank you Michael Carey

Edited: 18 Nov 2013, 8:20 p.m.


#5

Does it show up as a user variable ? If so, just highlight it and do a backspace to clear it.


#6

That got it!

Thank you Michael

#7

Quote:
Thank you for your quick reply Michael.

I get a "No such variable x."

I am using lower case x and in the CAS view, I tried all the obvious other combinations.

Thank you Michael Carey


If you created in the Home view, it will be listed in the Memory Browser. Press [Shift] [Toolbox] and select user variables. Then find 'x' and press the [<-] key. If you created x under CAS view, then use purge(x).

Sadly, 'x' created under Home view is different from 'x' created in the CAS view.


#8

You realize this goes against 25 YEARS of HP tradition.. perhaps longer?

Example:

90 Sto T                       90
T 90
purge(T) "No such variable T"

60 Sto t
Do you want to create a variable called t
OK
t 60
purge(t) "No such variable t"

80 Sto TT
Do you want to create a variable called TT
OK
TT 80
purge(TT) "No such varaiable TT

From the help page:

Syntax: purge(Var)
purge(varname) unassigns the variable varname

So, what exactly is purge() useful for?

Edited: 19 Nov 2013, 11:30 a.m. after one or more responses were posted


#9

In the first example, T is a predefined variable that cannot be deleted. In the last two examples, variables t and TT were created in Home view, and so are User variables that must be deleted by backspacing them. The purge() command is used to delete variables created in CAS view, which cannot be deleted by backspacing them. Press Shift Mem, and you will see separate entries for User Variables and CAS Vars.

Edited: 19 Nov 2013, 11:31 a.m.


#10

Thanks for the clarification. HP should print a poster with a flowchart explaining what is going on in this machine regarding variables.

This is so very, very frustrating... I'm not even allowed to store A=5_m^2 in this machine. I can have a=5_m^2, but not capital A... the variable used since caveman time to represent area ! This is just never going to work out well regarding units:

E=m*c^2 is not allowed, but e=m*c^2 is?
W=F*d is not allowed, but w=f*d is?

Unfathomable.


#11

Quote:
Thanks for the clarification. HP should print a poster with a flowchart explaining what is going on in this machine regarding variables.

This is so very, very frustrating... I'm not even allowed to store A=5_m^2 in this machine. I can have a=5_m^2, but not capital A... the variable used since caveman time to represent area ! This is just never going to work out well regarding units:

E=m*c^2 is not allowed, but e=m*c^2 is?
W=F*d is not allowed, but w=f*d is?

Unfathomable.


My understanding is that the Prime development can be boiled down to merging the HP38GII with XCas/Giac and placed inside nice hardware. While the hardware is nice, the problems arise from the fact that HP38GII and XCas/Giac use certain paradigms that are in direct conflict with each other. This is why everything got separated into "Home" vs "CAS" -- which may be useful to some -- but I find it annoying more often than not. So why merge these two systems anyway? My guess would be that they wanted to keep compatibility with the HP38GII.

I have no idea whether the HP38GII was ever a successful system -- I knew of its existence, but I had not seen one used ever by any of my students or any of the high school students who come to participate in various math competitions that are hosted annually. So I personally do not see why they feel obligated to keep compatibility.

Maybe the story is different outside the US where HP has a better market share.

From a design perspective, they should have just started with XCas/Giac (and if necessary, asked for a non-GPL license so they could create a private fork) and added a more robust interface to take advantage of the touch screen and colors. To summarize -- all the funding, energy, focus, etc. should have been put on making additions to XCas/Giac to make it more appropriate for a 320x240 screen and calculator keypad. Instead, it feels as though a lot of effort got put into trying to make two seemingly incompatible systems work nicely with each other at the cost of ... just about everything.


#12

Amen.

Couldn't have said it better myself.

I've already nicknamed my Prime "Frankenstein".

#13

Well, what HP has done is create predefined variables that are used globally and have specific types assigned to the. So A-Z,<theta> are always real numbers and Z0-Z9 are always complex numbers. You must create your own Home or CAS variables to assign other types. Now, there are advantages to this approach, as it allows you to access the global predefined variables anywhere in the calculator, so you can use them to pass information among different programs and Apps.


#14

Quote:
Well, what HP has done is create predefined variables that are used globally and have specific types assigned to the. So A-Z,<theta> are always real numbers and Z0-Z9 are always complex numbers. You must create your own Home or CAS variables to assign other types. Now, there are advantages to this approach, as it allows you to access the global predefined variables anywhere in the calculator, so you can use them to pass information among different programs and Apps.

What was the logic for implementing these predefined variables anyway? Is it because TI also does this with their TI83/84? If so, that's a terrible reason. I also hated this on the TI, too. What is truly sad is that many students who struggle with mathematics often have difficulty with abstraction. And it is further hindered by systems that force the idea that only certain variable names can be used for certain types of mathematical objects.

#15

In the 48,49,50 series calcs every variable is global and user-defined... and the user is therefore in complete control of their variables and equations. Works perfectly.

Why HP chose the most common variable names as internal to their apps is beyond me.

#16

Quote:
You realize this goes against 25 YEARS of HP tradition.. perhaps longer?

It's not just going against tradition -- it also defies logic in some instances. Why is a user being prompted to create a variable if the user clearly used the STO command? I can understand the prompting for deletion (and even in the case of deletion, I find the prompts annoying). However, it makes no sense when the user explicitly used STO, only to have the system then ask if that is what they want to do. If the variable already existed and the user wanted to overwrite it then a prompt seems appropriate (though still annoying).


#17

Actually, what I find far more annoying is the need to create all the variable names that will be used in the Solve or Function Apps, before you can enter an expression into their symbolic views. So, I had an expression timt=tima*e^(RA*<theta>*(1/Tema-1/Temt)), and I first had to go through the tedious process of creating all these variables except <theta>, which is a predefined real. You'd think the Apps would be smart enough to create these variable names as they were being entered.

Edited: 19 Nov 2013, 1:59 p.m.


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