HP50G and solving equations with complex numbers
02-28-2017, 03:00 AM
Post: #1
 jgharris Junior Member Posts: 3 Joined: Aug 2016
HP50G and solving equations with complex numbers
Am I correct that the HP50G cannot solve equations with complex numbers. For an easy example: V=I*Z where I=50A@-35 degrees and Z=(4,8) ohms? The calculator returns: Error: Bad Guess(es).

I saw somewhere searching online that one can use the MSLV command but that doesn't really work as a solver. Does a newer firmware fix this issue? I have Version: HP50-C Revision \$2.15 which I believe is the latest one.

I'm just shocked since I have used the HP35S for the past 8 years as my workday calculator (calculating CT/PT ratios, relay settings, etc.), to pass the F.E. and later the P.E. exam. On the P.E. exam I was even able to store equations such as symmetrical components (zero, positive and negative sequence) equations which of course require solving an equation with complex values as inputs and giving a complex number output. I'm shocked that the HP50G can't do this and the 35S can do this and more. According to my searches the release dates on the these two calculators was 2006 (HP50G) and 2007(HP35S). I know the 35s was designed to cater to colleges and to the NCEES exam standards which prohibits graphing calculators with qwerty keyboard entry and storage ability.

Not to beat a dead horse just surprised and wondering if I overlooked something and there is a way to solve equations with heavily involved complex numbers since I'm an EE and that's what we do...
02-28-2017, 04:07 AM
Post: #2
 Han Senior Member Posts: 1,882 Joined: Dec 2013
RE: HP50G and solving equations with complex numbers
Have you tried using the Solvesys library? http://www.hpcalc.org/search.php?query=solvesys

Graph 3D | QPI | SolveSys
02-28-2017, 10:11 AM
Post: #3
 Vtile Senior Member Posts: 406 Joined: Oct 2015
RE: HP50G and solving equations with complex numbers
Hmm... I can do it (v2.15). Although I just tried with the solve command and a random nonsolved equation.
10+j20 = ( 5+j5 ) * Z => 3+j

I think atleast if you only tried out some easy single function like impedance law, it is a user error.
02-28-2017, 12:16 PM (This post was last modified: 02-28-2017 12:18 PM by Gerson W. Barbosa.)
Post: #4
 Gerson W. Barbosa Senior Member Posts: 1,487 Joined: Dec 2013
RE: HP50G and solving equations with complex numbers
(02-28-2017 10:11 AM)Vtile Wrote:  Hmm... I can do it (v2.15). Although I just tried with the solve command and a random nonsolved equation.
10+j20 = ( 5+j5 ) * Z => 3+j

Of course simple equations like these can be solved simply by doing

(10,20) (5,5) ÷ --> (3.,1.)

Alternatively for more complex ones (pun not intended), we can use this program and do

'(10,20)=(5,5)*Z'
{Z}
SYS
Z --> (3.,1.)
02-28-2017, 12:26 PM
Post: #5
 Han Senior Member Posts: 1,882 Joined: Dec 2013
RE: HP50G and solving equations with complex numbers
(02-28-2017 03:00 AM)jgharris Wrote:  Not to beat a dead horse just surprised and wondering if I overlooked something and there is a way to solve equations with heavily involved complex numbers since I'm an EE and that's what we do...

Was complex mode enabled?

Graph 3D | QPI | SolveSys
02-28-2017, 01:39 PM (This post was last modified: 02-28-2017 01:57 PM by Vtile.)
Post: #6
 Vtile Senior Member Posts: 406 Joined: Oct 2015
RE: HP50G and solving equations with complex numbers
(02-28-2017 12:16 PM)Gerson W. Barbosa Wrote:
(02-28-2017 10:11 AM)Vtile Wrote:  Hmm... I can do it (v2.15). Although I just tried with the solve command and a random nonsolved equation.
10+j20 = ( 5+j5 ) * Z => 3+j

Of course simple equations like these can be solved simply by doing

(10,20) (5,5) ÷ --> (3.,1.)

Alternatively for more complex ones (pun not intended), we can use this program and do

'(10,20)=(5,5)*Z'
{Z}
SYS
Z --> (3.,1.)
Of course, it were just test of given example.

[V1 - V2 = 10*Ix
V1/j20 + (V1 - V3)/20 + V2/10 + (V2 - V3)/-j10 = 0
V3/j10 + (V3-V2)/-j10 + 2<45deg + (V3 - V1)/20 = 0
Ix = -V3/j10]
[V1 V2 V3 Ix]
SOLVE

Can be used for system of complex equations, but I don't know the limits of the solve command, it seems to have odd pitfalls at times.

One question is are the OP after a numerical solver with complex numbers as by definition (numerical) it should also do single equations with complex input. I haven't tested and I have no time just now to play it around to see if it is possible somehow. Edit. Yes, numerical solver do not like complex input and gives the "bad quess" error, I'm suprised actually.
02-28-2017, 07:22 PM
Post: #7
 Vtile Senior Member Posts: 406 Joined: Oct 2015
RE: HP50G and solving equations with complex numbers
Rather interesting the Num.slv/SOLVE EQUATION do list a complex number as a valid type, but can't solve for them. Is that a bug / feature of the recent firmware or is it something that never got implemented? . ..Or is it dependaple from certain flag settings etc. to work.
02-28-2017, 08:25 PM
Post: #8
 jgharris Junior Member Posts: 3 Joined: Aug 2016
RE: HP50G and solving equations with complex numbers
[Was complex mode enabled?]

Yes, I went into CAS and tried enabling and turning off the complex settings as well as the exact/approximate and verbose and other settings (I don't have the calc with me since I'm still at work...). No change, same error.

I was hoping that the HP50G would be able to do this without any external programs.

When I say using an equation solver i mean being able for the calculator to store a library of equations in memory and then when you want to solve for a variable in chosen equation you select the variable to solve for and the calc will prompt you for each variable input in the equation [1 equation, 1 unknown...]. For an easy example we can calculate the positive sequence current of an unbalanced load/fault: P=(1/3)*(A+a*B+a^2*C), where a=1@120 degrees and a^2=1@240 degrees. On my HP35s I can enter that equation then hit solve (it prompts me for what variable I want it to solve for, in this case P) and it then prompts me for all of the remaining variables/unknown constants in the equation. So for the case where A=120A@-18deg, B=960A@-191deg, C=120A@-326deg my beloved HP35s quickly spits out the answer for P which is: P= 383A@-67.7 deg.

Like I said not to beat a dead horse I am just suprised that my fancy graphing calculator struggles to do this type of calculation without a 3rd party program. Not only is the HP35s capable of doing this, it is able to hold dozens of equations which is really helpful in a pinch for the working engineer.
03-04-2017, 11:21 PM
Post: #9
 Simone Cerica Member Posts: 60 Joined: Mar 2014
RE: HP50G and solving equations with complex numbers
To solve systems of linear equations with complex coefficients you can use both LINSOLVE and SOLVE:

Code:
[ '(1+i)*X-Y=i' '(1-i)*X+(1+i)*Y=1' ] [ 'X' 'Y' ] LINSOLVE

returns

Code:
{ [ '(1+i)*X-Y=i' '(1-i)*X+(1+i)*Y=1' ] [ 'X' 'Y' ] } :Specific: { '1+i' 1 1 1. } [ 'X=(1+i)/2' 'Y=0' ]

to solve single equations numerically you can operate directly on the stack:

to enter complex numbers in polar form can be useful these programs:

Code:
\<< \-> X Y \<< { X Y } XNUM EVAL DEG -19. SF CYLIN \->V2 \>> \>> 'PN' STO

syntax: "module r" "argument φ" PN --> (r,\<)φ)
ex: '\v/2' 45 PN --> (1.41421356237,\<)45.)

Code:
\<< -16 FS? IF THEN -16 CF ELSE -16 SF END \>> 'RP' STO

RP switches from rectangular to polar notation and vice versa:
(1.,1.) RP --> (1.41421356237,\<)45.)
(1.41421356237,\<)45.) RP --> (1.,1.)

however, for more complex equations and non-linear systems for better use SolveSys as suggested by Han:

SolveSys 49 1.2
http://www.hpcalc.org/details/3145
SolveSys 49 Documentation
http://www.hpcalc.org/details/3146

Furthermore I strongly suggest you read the Complex Numbers Marathon: http://www.hpcalc.org/details/5114

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