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03-24-2014
08:42 AM

03-24-2014
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

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03-24-2014
08:48 AM

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03-24-2014
08:57 AM

03-24-2014
08:57 AM

Re: Using SOLVE function with 4 equations

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.

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03-24-2014
09:09 AM

03-24-2014
09:09 AM

Re: Using SOLVE function with 4 equations

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

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03-24-2014
09:15 AM

03-24-2014
09:15 AM

Re: Using SOLVE function with 4 equations

Seems like there are no solutions for this system.

Is it correct?

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03-24-2014
09:22 AM

03-24-2014
09:22 AM

Re: Using SOLVE function with 4 equations

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.

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03-24-2014
09:18 AM

03-24-2014
09:18 AM

Re: Using SOLVE function with 4 equations

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

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03-24-2014
09:23 AM

03-24-2014
09:23 AM

Re: Using SOLVE function with 4 equations

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

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03-24-2014
09:32 AM

03-24-2014
09:32 AM

Re: Using SOLVE function with 4 equations

Werner, I just opened your file.

Why did I receive this error?

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03-24-2014
09:45 AM

03-24-2014
09:45 AM

Re: Using SOLVE function with 4 equations

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?

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03-24-2014
09:55 AM

03-24-2014
09:55 AM

Re: Using SOLVE function with 4 equations

Version 14.0.0.163

It's the capital BETA.

It can be found at the Greek Symbol Toolbar.

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03-24-2014
10:14 AM

03-24-2014
10:14 AM

Re: Using SOLVE function with 4 equations

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

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03-24-2014
10:35 AM

03-24-2014
10:35 AM

Re: Using SOLVE function with 4 equations

It's the capital BETA.

Ah! Tricky!

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03-24-2014
01:41 PM

03-24-2014
01:41 PM

Re: Using SOLVE function with 4 equations

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

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03-24-2014
02:07 PM

03-24-2014
02:07 PM

Re: Using SOLVE function with 4 equations

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.