HP Prime "Cannot Find Solution" when solving two equations

[DGRCarter]

I am trying to solve only two equations using the Solve App and it fails at every attempt. I just updated to latest firmware 20181016. The equations are super simple algebra:
S=(P*L*C)/I
I=pie/64*(D^4-E^4)

I made sure all the variables are in the system already. It will solve them individual, but not both at the same time. I tried this on my sons HP Prime with firmware: 20170710 and it worked two times, then stopped as well with the "Cannot Find Solution".

I also tried it on the emulator on my windows PC without any luck. Same issue.

Do I have a setting that is off or set incorrectly?
Any help would be greatly appreciated.

Thanks,
Geoff

[rprosperi]

(04-21-2019 12:15 AM)DGRCarter Wrote:  Do I have a setting that is off or set incorrectly?
Any help would be greatly appreciated.

Thanks,
Geoff

Geoff - describe how you tried to solve these; from which mode (home/CAS) and which commands you tried, and the results expected and received. Also, if there are settings you suspect may be incorrect, state how those are set. With this info, it will be much easier to help you; as stated there are just too many possibilities.

[DGRCarter]

Ideally, it would solve both equations simultaneously in the Solve App in either CAS or Home.

If i hit the solve button between 10-20 times it will eventually solve simultaneously. Also, if I remove the exponents from "D" an "E" it will solve right away.

I think its in the software...

[Aries]

If I'm not mistaken, there are 8 unknowns, they're a number !

[DGRCarter]

Hi Aries,

You are right those are numbers. I could plug in all the variables and solve them individually. But that defeats the purpose of solving multiple equations simultaneously and optimizing on a solution. These are parameters that can be changed to solve for different values of I and S quickly. I was able to solve multiple equations on the HP50 with a simple program. I thought that is what the Solve App is for, right?

[ijabbott]

My guess is that on the HP 50g you would use the Multiple Equation Solver (MES) to solve those equations, but the HP Prime's Solver is used to solve a system of equations (simultaneous equations). They are not the same thing, and the equations you have are not a system of equations. The 50g's MES solves the equations one at a time, not simultaneously.

[DGRCarter]

Ah, well that makes more sense. I thought the Solve App was the same as the 50g Solve command. It eventually does solve, after a number of attempts though. It does usually work to solve multiple equations but starts to fail when there are exponents.

Thanks for clearing that up for me. I really thought it was the calculator.

[ijabbott]

(04-21-2019 09:59 PM)DGRCarter Wrote:  Ah, well that makes more sense. I thought the Solve App was the same as the 50g Solve command. It eventually does solve, after a number of attempts though. It does usually work to solve multiple equations but starts to fail when there are exponents.

Thanks for clearing that up for me. I really thought it was the calculator.

It was just a guess, not any sort of official explanation.

Since the Prime doesn't offer any manual control over a strategy for solving multiple equations, it ought to figure it out by itself.

[DGRCarter]

Seems like a tragedy to give up the MES capability...

[ndzied1]

(04-22-2019 08:48 PM)DGRCarter Wrote:  Seems like a tragedy to give up the MES capability...

Patent is expired... you could write you own ;-)

https://patents.google.com/patent/US5175700

[Aries]

I'd like to know what procedure was followed … the steps the user did … the result expected and so

[StephenG1CMZ]

(04-22-2019 08:48 PM)DGRCarter Wrote:  Seems like a tragedy to give up the MES capability...

Just in case anyone hasn't seen it, there's an old thread suggesting another approach to MES on the Prime. https://www.hpmuseum.org/forum/thread-95...ion+solver

[DGRCarter]

Hi Aries,

The way I thought the solve app works was this:
1. Put in your equations, up to 10.
2. Check the ones you wish to solve for
3. go the solver numeric view
4. check the parameters you wish to solve for - must be the same number of parameters as equations.
5. Solve for the missing parameters

It would go through and solve them in the order required to find a solution. This was a really great feature on the HP 48GX, 50G calculators. Really powerful and you could run through scenarios quickly. This does work to some extent on the Prime, but fails when higher powers are used in the parameters. Not quite as robust as the older versions. Mathcad does this great, but it would be nice to have this on a portable.

StephenG1CMZ,

Thanks for the link!

[CyberAngel]

(04-21-2019 09:05 PM)ijabbott Wrote:  My guess is that on the HP 50g you would use the Multiple Equation Solver (MES) to solve those equations, but the HP Prime's Solver is used to solve a system of equations (simultaneous equations). They are not the same thing, and the equations you have are not a system of equations. The 50g's MES solves the equations one at a time, not simultaneously.

I recall faintly that once upon a time I requested this for the HP 50G
and professor Bernard Parisse wrote
MSLV
or similar.
It does solve for two variables quite quickly , three slowly
You need to check the HP Manuals ...
wait, I found an old document:
https://www.hpcalc.org/hp49/docs/misc/cccs200.zip
which is still very useful.
I wonder who would ever use his time and effort to compile such an exhaustive worksheet?
VPN

[dae]

I put these 4 equations into Solver, and it reported "Cannot find solution"

A-B=7
2*B+3*B-3*C+B-A=0
X*C+2*C-7+3*(C-B)=0
B=2.273

I replaced the 3rd equation (starting X*C) with one isolating X to the left
of the equal sign, and it solved the equations.

I went back to the original 3rd equation, removing the changed
equation, and this time it solved.
Why would it not solve one time, but solve another time?

I had the same results using the physical Prime G2 and the virtual unit.

[Carsen]

Hi dae,

What do you mean by Solver? There are many solver commands in the Prime, so specifying will help us help you.

Did you try using the fsolve() command in the CAS environment? I typed in the 4 equations you posted as is and I got the 4 solutions with no error messages. Maybe this is the command you are looking for.

Best!

[dae]

I meant to say the "Solve" app, which uses E0 to E9. Sorry for the confusion.

[Carsen]

Okay. I think the reason why you are getting an error message is because you have bad guess(es) entered in A, B, C, and/or X. The Solve App takes the current numbers assigned to the variables and uses them as guesses.

Enter 5's in A, B, C, and X. Then press solve. HP Prime should give you the correct answers with no troubles because you input better guesses.