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Mar 24, 2014
08:42 AM

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Mar 24, 2014
08:42 AM

Using SOLVE function with 4 equations

Hi,

I would like to determine 4 variables with equations but it's returning (0, 0, 0, 0) which is not correct.

I think the way I placed the equations is not right.

Can anyone help me with this?

Thanks!!

14 REPLIES 14

Mar 24, 2014
08:48 AM

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Mar 24, 2014
08:57 AM

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Mar 24, 2014
08:57 AM

For the symbolic "solve", the equations must be put in a vector, not a program structure.

As it seems you are just searching for a numeric answer, you may also consider using a Given-Find() solve block instead.

Mar 24, 2014
09:09 AM

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Mar 24, 2014
09:09 AM

You are trying to solve for eight unknowns (the real and imaginary parts of B1, C1 etc) with only four equations.

Plus, what Werner said.

Alan

Mar 24, 2014
09:15 AM

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Mar 24, 2014
09:15 AM

Seems like there are no solutions for this system.

Is it correct?

Mar 24, 2014
09:22 AM

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Mar 24, 2014
09:22 AM

Max Gomes wrote:

Seems like there are no solutions for this system.

Is it correct?

Yes, unless you assume that the variables are real numbers 😉

See below.

Mar 24, 2014
09:18 AM

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Mar 24, 2014
09:18 AM

From the way the equations are set up I guess we have to assume that the solved for variables should be real valued

Mar 24, 2014
09:23 AM

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Mar 24, 2014
09:23 AM

Another possibility is to set all the imaginary parts to zero to give four more equations, but this depends on what the system of equations represents.

Alan

Mar 24, 2014
09:32 AM

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Mar 24, 2014
09:32 AM

Werner, I just opened your file.

Why did I receive this error?

Mar 24, 2014
09:45 AM

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Mar 24, 2014
09:45 AM

Not sure what happens here. I just loaded my file from my post and it works OK and shows what my screenshot shows.

One thing I noticed when i worked on your file was that the B's in your file are not "normal" B's but the style of those variables is still "normal"!?. They look bold (you can see it on my first screenshot) and I have no idea how you created them. maybe retyping all variable names cures the problem.

Which version of Mathcad are you using?

Mar 24, 2014
09:55 AM

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Mar 24, 2014
09:55 AM

Version 14.0.0.163

It's the capital BETA.

It can be found at the Greek Symbol Toolbar.

Mar 24, 2014
10:14 AM

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Mar 24, 2014
10:14 AM

Max Gomes wrote:

Version 14.0.0.163

It's the capital BETA.

It can be found at the Greek Symbol Toolbar.

I've just run Werner's worksheet in M14.0.0.286 and it works as shown in Werner's message.

Stuart

Mar 24, 2014
10:35 AM

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Mar 24, 2014
10:35 AM

It's the capital BETA.

Ah! Tricky!

Mar 24, 2014
01:41 PM

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Mar 24, 2014
01:41 PM

Werner,

I've added one more equation to the system, could you please open in your Mathcad to check if it still has solution?

Thanks

Mar 24, 2014
02:07 PM

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Mar 24, 2014
02:07 PM

I've added one more equation to the system, could you please open in your Mathcad to check if it still has solution?

No, it hasn't. Five equations but just 4 variables to solve for - you must have great luck for an overdetermined system to get solved. Mathcads symbolic solver is especially sensitive wrt over- but also underdetermined systems.

What are you trying to do here?

Would a "best fit" (least sq.error) be an option? So you might try a numeric solve block with minerr or minimize.