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kriley1-Visitor
1-Visitor
December 16, 2015
Solved

Need help with a solver block

Hello,

I need some help with a solver block. I have attached the .mcdx fill. I'm trying to solve for 3 variable with 4 equations (constraints) which are a function of theta.

I feel I'm going about this wrong.

Any help is greatly appreciated,

Ken

Werner_E
Werner_EAnswer
25-Diamond I
December 17, 2015

I, too, can't read your 3.1 file, but fortunately Luc has posted a picture.

As Luc already pointed out you can omit one of your last three equations which is fine, as so you have just an ordinary system of three equations in three variables.

Using a solve block you have to provide values for all variables other than the variables you are solving for.

Obviously those values are missing in your sheet, so lets use the symbolics.

Unfortunately in Prime we are not allowed to evaluate a solve block symbolically, so we have to use  the symbolic solve to do the job.

Here its done in Mathcad 15, but it should work the same in Prime:

Werner

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7 replies

RichardJ19-Tanzanite
19-Tanzanite
December 16, 2015

I can't read your file because it's in Prime 3.1 format, but in general there is no solution to a system of 4 equations with only 3 unknowns (it's an over determined system). You either need to get rid of one equation, or find one more unknown.

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LucMeekes23-Emerald V
23-Emerald V
December 16, 2015

I'm afraid 3 of the 4 equations aren't independent:

Your first equation may be OK, But the other three say:

Mc*Xc=Me*Xe, Mc*Xc=Mr*Xr, Me*Xe=Mr*Xr

The second and the third already imply the fourth. Omit that one.

What about those functions V(theta)? How should the solver know/find out about them. And who is Vr?

Then in the solver, your putting yet another equation (=), rather than an assigment or just an evaluation (:=)

And with M(theta) multiplied with the vector: Note that you cannot assign someting to a multiplication.

Normally you would write in the solver something like:

Success!
Luc.

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ValeryOchkov24-Ruby IV
24-Ruby IV
December 17, 2015

And what about minerr not find function?

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Werner_E
Werner_E25-Diamond IAnswer
25-Diamond I
December 17, 2015

I, too, can't read your 3.1 file, but fortunately Luc has posted a picture.

As Luc already pointed out you can omit one of your last three equations which is fine, as so you have just an ordinary system of three equations in three variables.

Using a solve block you have to provide values for all variables other than the variables you are solving for.

Obviously those values are missing in your sheet, so lets use the symbolics.

Unfortunately in Prime we are not allowed to evaluate a solve block symbolically, so we have to use  the symbolic solve to do the job.

Here its done in Mathcad 15, but it should work the same in Prime:

Werner

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kriley1-VisitorAuthor
1-Visitor
December 17, 2015

Thanks everyone for the help!

I've gotten the following to work if I put in a value for theta in Vc( ) and Ve( ). Vc and Ve are functions of theta defined earlier in the worksheet.

Can I use a function such as Vc( ) in the solver block?

Ken

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kriley1-VisitorAuthor
1-Visitor
December 17, 2015

I understand what Werner is saying. You do have to provide values for all the variables in the solver block. Let me try the symbolic approach as Werner has suggested

Thank you Werner,

Ken

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kriley1-VisitorAuthor
1-Visitor
December 17, 2015

Think everyone for the help. I was able to work the problem using symolics.

Ken

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