solve app question

[roadrunner]

The solve app doesn't appear to be solving multiple equations with version 10077. In the emulator here is what I do:

1. Reset the solve app, then start it;
2. Type A=B+C into E1 and B=C+D into E2;
3. Press the Num key;
4. Check A and B, uncheck C and D;
5. Type in 7->A, 5->B, 2.1->C, 3->D;
6. Tap Solve and I get a "Cannot find solution" error.

   

Typing in different seeds doesn't help even seeding A and B with the correct answer doesn't help. When I solve each equation separately I get the correct answer.

When I do the exact same thing on the handheld and on another pc, both running 8151, everything works as expected.

   

Based on another thread I posted earlier today nobody else on this forum seems to be having this problem. What could I be doing wrong? Am I overlooking some obscure setting, or just dense?

-road

[DrD]

If you are seeing check boxes in the Solve Numeric View, your version of this app is different than mine, (Per your screen caps). First solve for B, then solve for A ...

Solve App:

1. [Symb] to enter equations
2. E1: A=B+C [Uncheck box]
3. E2: B=C+D [Check box] // to solve this equation first ...

4. [Num] to enter known values
5. Put 2.1 in C:
6. Put 3 in D:
7. Press [Solve] soft key (B: is active box at this point.)
8. B: reports 5.10 // Computed value for B

9. [Symb] to select other equation
10. E1: [Uncheck box]
11. E2: [Check box]

12. [Num] to solve last equation
13. Press [Solve] soft key (A: is active box at this point.)
14. A: reports 7.20. // Computed value for B+C

A=B+C ==> A=5.10 + 2.10 ==> 7.20 ==> Q.E.D.

[roadrunner]

Thanks for your reply DrD,

The method you suggested works here as well. Version 8151, however, would solve both equation simultaneously. With both E1 and E2 checked you could press Num type 2.1 in C and 3 in D, tap solve and you get the answer for A and B in one operation. I just didn't expect that ability to be removed in 10077.

Thanks again for your help.

-road

[Tim Wessman]

Nope, looks like you've found a problem. Basically, the allowed result length is incorrectly being dependent on the length of the result itself. If the result was longer then 3-4 digits, you'd get a result here. Shorter, and none will show up even though internally it is calculated correctly. The tests in our suite for multiple equation solving did not catch this because they were all "real world" ones with not-nice, simple and short answers. :-(

It is on the list for correction. Thanks!

[Helge Gabert]

It would also be useful to have a flag (info softkey: zero?) for the case of multiple simultaneous equations, like for the case of a single equation.

Better yet, scratch the solve app and replace it with something akin to Solvesys for the HP50G. A solver that can also deal with non-linear equations, and complex solutions!

[kruki]

Hi
I can confirm that I have the same problem on my HP Prime emulator for android.
I get the correct answer only if I solve each equation separately or use longer numbers with 3-4 digits like Tim Wessman said. I also search for program like "solvesys" for HP49/50 but I haven't managed to find it so far. I truly hope that this issue will be fixed with the next update.

[Helge Gabert]

Check out

http://www.hpcalc.org/search.php?query=solvesys

Go to solvesys 49 1.2

[retoa]

(04-26-2016 01:25 PM)DrD Wrote:  If you are seeing check boxes in the Solve Numeric View, your version of this app is different than mine, (Per your screen caps). First solve for B, then solve for A ...

Solve App:

1. [Symb] to enter equations
2. E1: A=B+C [Uncheck box]
3. E2: B=C+D [Check box] // to solve this equation first ...

4. [Num] to enter known values
5. Put 2.1 in C:
6. Put 3 in D:
7. Press [Solve] soft key (B: is active box at this point.)
8. B: reports 5.10 // Computed value for B

9. [Symb] to select other equation
10. E1: [Uncheck box]
11. E2: [Check box]

12. [Num] to solve last equation
13. Press [Solve] soft key (A: is active box at this point.)
14. A: reports 7.20. // Computed value for B+C

A=B+C ==> A=5.10 + 2.10 ==> 7.20 ==> Q.E.D.

This works only if the unknowns variables are A and B.
What would you do with B and C as unknown? You can not solve any of the two equations alone...

[kruki]

Thanks Helge Gabert for link but I meant solvesys (or silimilar program) for HP Prime. I have an old HP48G and often used solvesys.

DrD Wrote try to insert known numbers in form with more digits for example put C=2.10001 and D=3.00001, check box E1 and E2 and you will be able to solve both equation simultaneously.

Sorry for my bad english but it is not my native language.

[Helge Gabert]

Alas, there is no solvesys for Prime. My hope is that the prime solve app will evolve into something like solvesys for the HP 50G!

fsolve, of course, is very capable, but it lacks the menu interface, and it doesn't appear that you can allow complex solutions for only certain variables (check complex on/off).