[BUG] HP 50g SOLVE/SOLVR menu does not display unknown var  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: [BUG] HP 50g SOLVE/SOLVR menu does not display unknown var (/thread196704.html) 
[BUG] HP 50g SOLVE/SOLVR menu does not display unknown var  François Vanzeveren  09202011 Hello
I think I found a bug in the SOLVER application. My VERSION: Version HP50C 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.
Re: [BUG] SOLVE/SOLVR menu does not display unknown var  C.Ret  09202011 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 ].
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. In Hp28C/S, the change fro [ x ] to [ n ] (or disappearance) is immediate, perhaps the 'bug' on HP50g 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
Re: [BUG] SOLVE/SOLVR menu does not display unknown var  François Vanzeveren  09202011 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.
Re: [BUG] SOLVE/SOLVR menu does not display unknown var  C.Ret  09202011 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 gasphase 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, m^{3}, 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.
