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How to use mathcad to symbolically extract variables-3

ChadG.
1-Newbie

How to use mathcad to symbolically extract variables-3

Ok I am trying these but Mathcad is crashing on me

It used to give me a message that the solution is too big to display but not any more

http://communities.ptc.com/message/182372#182372

Is there a way I can store the symbolic calculation into an array as in:

http://communities.ptc.com/message/182371#182371

without calculating it then finding the elements one by one as LucMeekes did

16 REPLIES 16
AlanStevens
15-Moonstone
(To:ChadG.)

Chad G. wrote:

Ok I am trying these but Mathcad is crashing on me

It used to give me a message that the solution is too big to display but not any more

http://communities.ptc.com/message/182372#182372

It still works ok for me, giving the "too big to display" message, but not crashing. Have you made any changes?

Is there a way I can store the symbolic calculation into an array as in:

The only way I can think of is to copy each individual element and paste into a 4x1 vector.

Alan

I mean store elements directly without the "too big to display" since I do not need that whole answer

which I do not know why it crashes the computer I have not done changes

RichardJ
19-Tanzanite
(To:ChadG.)

Ok I am trying these but Mathcad is crashing on me

It used to give me a message that the solution is too big to display but not any more

Try repairing your Mathcad installation.

Is there a way I can store the symbolic calculation into an array as in:

http://communities.ptc.com/message/182371#182371

without calculating it then finding the elements one by one as LucMeekes did

Maybe I misunderstand what you are asking for, but if you have not calculated it then there is nothing to store.

here is the crash message

Problem signature:

Problem Event Name: APPCRASH

Application Name: mathcad.exe

Application Version: 14.0.0.163

Application Timestamp: 45ba2610

Fault Module Name: KERNELBASE.dll

Fault Module Version: 6.1.7601.17651

Fault Module Timestamp: 4e211319

Exception Code: e053534f

Exception Offset: 0000b9bc

OS Version: 6.1.7601.2.1.0.768.3

Locale ID: 1033

RichardJ
19-Tanzanite
(To:ChadG.)

Sorry, the crash message means no more to me than it does to you.

As far as the worksheet goes, what you are trying to do will not work. When Mathcad sees a numeric assignment the first thing it does is check that all the variables on the RHS are defined. If that's not the case then the assignment is ignored and you get an error. So when Var is passed to the symbolic processor, there is no connection between it and the variable names in the vector. It simply tries to solve for "Var", and of course can't.

I am simply redoing what LucMeekes did (he did it in an older version of mathcad)

http://communities.ptc.com/message/182371#182371

If you say I cannot do this maybe that's why mathcad is crashing

RichardJ
19-Tanzanite
(To:ChadG.)

I am simply redoing what LucMeekes did (he did it in an older version of mathcad)

http://communities.ptc.com/message/182371#182371

Luc has version 11. The compute engine was rewritten going from version 11 to version 12, so what works in MC11 does not necessarily work in later versions. If you remove the numeric assignment (i.e. Sols:=), which is not allowed in MC11, yes, your worksheet works (I just tried it). But it will not work in version 12 or later.

If you say I cannot do this maybe that's why mathcad is crashing

Exactly which version are you running (including service releases)?

I am running Mathcad 14.0.0.163, any other way to overcome this. I am just trying to write the equations in the form

http://communities.ptc.com/message/182371#182371

RichardJ
19-Tanzanite
(To:ChadG.)

Chad G. wrote:

I am running Mathcad 14.0.0.163,

Download and install the latest service release you can get (probably M020)

I am just trying to write the equations in the form

http://communities.ptc.com/message/182371#182371

Sorry, but that is not clear. Do you mean the form shown in Wayne's post?

Sorry for the confusion. I mean writing the following equations in the form

My transfer matrix.jpg

AlanStevens
15-Moonstone
(To:ChadG.)

Do you mean like the attached?

Alan

Thanks Alan, I do not understand the M matrix in your file (how did you find it? I am actually looking for it). I am trying to find the M matrix as in the following

My transfer matrix.jpg

whether it is the multiplication of two other matrices. All I am trying is to isolate Var in one side of the equation and Var0

AlanStevens
15-Moonstone
(To:ChadG.)

Chad G. wrote:

Thanks Alan, I do not understand the M matrix in your file (how did you find it?

In each equation collect together the terms that multiply ur+, ur- etc. These form the conponents of the matrix M (as I did this rather quickly I might not have written them all down correctly - you should check). Because of the way your equations are written, this matrix multiplies both the vector of Var terms and that of the Var0 terms. This means your equations can be written in matrix form as M*Var-M*Var0 = V where V is the vector of terms a, b, c and d (you don't list a, b, c and d in your picture above, but they are in your original worksheet). This equation can be rewritten as Var = Var0 + inverseM*V.

Alan

Attached shows a systematic way of getting Mathcad to generate M automatically.

Alan

Thanks a lot and excellent, I understand what you are trying to do (in general) however I do not think the coefficients matrix for Var would be the same as Var0

To be more specific I did not understand the for loop

AlanStevens
15-Moonstone
(To:ChadG.)

Chad G. wrote:

... I do not think the coefficients matrix for Var would be the same as Var0

You are right. It shows I should have been systematic in using Mathcad to generate the cofficients of both Var and Var0 instead of making the assumption they were the same!

To be more specific I did not understand the for loop

See attached , which contains a more detailed explanation of the for loop.

Alan

Edited: Sign corrected in attached file

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