[BUG] HP 50g SOLVE/SOLVR menu does not display unknown var



#2

Hello

I think I found a bug in the SOLVER application.
This bug is reproducible also in the HP 50g emulator.

My VERSION:

Version HP50-C

Revision #2.15

Copyright HP 2009

Description of the bug

1. Put an equation into the variable EQ (eg. COS(X)).

2. If the variable 'X' exists, purge it.

3. Enter the SOLVE/SOLVR menu.

At that point everything seems ok, the menu displaying two items: 'X' and 'EXPR='

4. Enter a real number into 'X' (ex: 2) and press 'EXPR='. You get -.4161...

5. Press the VAR key to return to your home directory. You see the 'X' variable created.

6. Return to the SOLVE/SOLVR menu. No problem, both items ('X' and 'EXPR=' are still visible)

7. Now enter the symbolic value '2*pi' (using the greek letter for pi) into 'X' and press 'EXPR='. You get 1.

8. Press the VAR key to return in you home directory.

9. Return back to the SOLVE/SOLVR menu.

SURPRISE!!! The 'X' variable is no more displayed and accessible...

If you want to have it displayed and accessible, you have to enter non symbolic value!

I guess it has been already noted by some... Anyone knows if this has been notified to HP?

Regards

François

Edited: 20 Sept 2011, 6:13 a.m.


#3

Bonjour François,

It's not a 'bug', it is a feature of the RPL solver.

The [ X ] disappear from the solver menu as soon as there no more adjustable variable in the expression.

If you store '2*PI*n' in variable 'X' instead of just '2*PI', you will see that [ X ] menu is replace by [ n ].
The solver menu only list variable, no constant of the stored EQ-expression.

Oppositely, if you store in the variable 'X' [... edited ...] a program (i.e. « 2 PI * » ) you will observe again that the [ x ] disappear from the solver menu.
If you PURGE the variable ‘X’, the [ X ] will immediately reappearing in the Solver menu.

In Hp-28C/S, the change fro [ x ] to [ n ] (or disappearance) is immediate, perhaps the 'bug' on HP-50g is due to display latency (or a missing refresh cycle is this case). Is that why you notice it only by swapping from and back to the solver menu?


Edited: 20 Sept 2011, 7:00 a.m. after one or more responses were posted


#4

Thanks C.Ret

Looks as a functionality, indeed :)

Nevertheless, if I store in the variable 'X' a non symbolic constant, the [X] appears well in the solvr menu...

It is only when I store symbolic constant that it does not appear.

Cheers

François

Edited: 20 Sept 2011, 6:33 a.m.


#5

Your right, I miss this point, using a constant, the [ x ] remain in the menu.

This is a trick I often used, to make physical or chemistry constant out of the solver menu, you simply have to enter the constant quote by « and ».

For example, suppose you have to investigate pressure and volume changes of a gas-phase reactor. Admitting your gas is considered as ideal, you may use the equation of state :

As soon as you enter this equation, [ P ][ V ][ n ][ R ][ T ] show up in the solver menu. As the gas constant R will not change and you will only consider change in pressure, volum and temperature. The trick is to store «8.314 » in ‘R’ so that you may input P, V, n and T in respectively Pa, m3, mol and °K. [ R ] disappear from the solver menu.

Storing ‘273.15+t’ in ‘T’ makes [ t ] to replace [ T ] in solver menu and allow you to use temperature in Celsius.


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