Solve This Linear System HP50g

[rbridges]

Hi guys,
I am an Electrical Engineer and have to solve systems of linear equations on a regular basis, so that functionality is very important for me. Everything works fine 95% of the time, but sometimes I run into systems that the HP50g does not seem to like. For instance the one below.

I want to solve for x,y,z, and a in terms of V

V-100000x+100000y-100000x=0
-250000y-V+100000x+100000z=0
-250000z+100000a+100000y=0
-250000a+100000z=0

After these 4 equations are on the stack, I make them into a vector by pushing {4} onto the stack and then pressing ->ARRY. Then I push the variables I want to solve for onto the stack, x,y,z, and a and make a vector out of them. Then I use LINSOLV to solve the system. However, when I do it this way, the calculator gives me an equation for x, an equation for y, and 2 equations for z, and no equation for s. I am not sure what I am doing wrong. Is there some other way to do this that would yield me 4 equations, one for each variable I want to solve for in terms of V?

If my method for solving linear equations is confusing in any way, I basically followed this video
http://www.youtube.com/watch?v=z802L29JyQE

Thanks in advance.

[BartdB]

Hi,

Try using SOLVE instead (in the S.SLV menu (White LeftShift 7), choose "6. Solve" or F6 if using soft menus).

Also see Chapter 7 of the 887-page  HP-50G User's Guide.

Original arrays:

Solutions using SOLVE:

Hope this helps.

[Maké]

Hi!, rbridges:

Welcome, to Forum!.

Please, try with this examples ... http://50gtutorials.blogspot.com.ar/2009/10/solving-systems-of-equations-on-hp-50g.html

[rbridges]

Hey thanks so much for the reply Bart!
When I use your method, the calculator gives me an error saying "not exact system." 
What am I doing wrong?

[BartdB]

Hi,

In settings MODE -> CAS make sure "_Numeric" and "_Approx" are both UNchecked (otherwise the solver searches for numeric only solution, but you require a symbolic solution containing V).

Side note: you probably noticed I had my setting in "Vertical vector display" mode. Hope it didn't confuse you (it is set with MODE -> Flags and check 98).

Hope this helps.

[rbridges]

Hey Bart.
Thanks so much. That worked for me!

Now while I have your attention I figured I would try to ask one more question if I may.

I am now trying to solve equations with complex variables in them. This following example is much more simple than the types of equations I am trying to solve, but it highlights the problem I am having:

4 + j3x = 4 + j7

To solve this simple equation for x by hand, one would simply set 3x = 7 and solve for x. This would give x = 2.3333

When I attempt to enter the left hand side of this equation on the HP50g, I do the following

1. open parenthesis
2. 4 SPACE 3x
3. enter

And then the calculator gives me a syntax error at the "x" 
The calculator doesn't seem to like when I try to enter variables inside of the complex number.

How could I go about solving something like this?

[BartdB · Accepted solution]

Hi,

Not sure exactly how you're entering it, so I'm being explicit just to b certain:

Notes:

1) as an equation is being entered, use ' '

2) it is better to use a comma to separate real and imaginary parts

3) use explicit multiply

so the entry will look like:

'(4,3*X)=(4,7)'

For this simple equation and assuming X is defined as the independent variable (shown as 'X' in the middle top of the screen), you can use SOLVEVX for this one: (no. 5 in S.SLV menu or F5 if using soft-keys)

with "_Approx" unchecked the answer is:

X=7/3

with "vApprox" checked the answer is:

X=(2.333333333,0)       (although X is part of the imaginary number, it itself is a real number).

Regards.

[rbridges]

Thanks so much!