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ptc-45285571-Visitor
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April 3, 2012
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Problem with inverting a symbolically matrix

  • April 3, 2012
  • 1 reply
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Hallo

I have trouble to invert a [8x8] Matrix symbolically.

Mathcad starts to invert the Matrix but even after hours (if Mathcad doesn´t crash before) it doesn´t finish the calculation.

There is one unknown variable "ϕr" in it, could this be the reason why Mathcad can´t finish the calculation?

Please have a short look at my Mathcad File for better understanding.

I´m using Mathcad 15 and the Matrix i´d like to invert is named " Nr(ϕr)" at the bottom of the calculation.

I am very grateful for any help.

Best answer by AlanStevens

Nr evaluates ok (at least it does in my M15). It shows in red because the result is too large to display. However, the result can be used in further expressions below. The final expression works also, as long as you don't insist on a symbolic result - see attached. Do you really need all those symbolic solutions? Wouldn't numerical results be adequate?

Alan

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AlanStevens19-TanzaniteAnswer
19-Tanzanite
April 3, 2012

Nr evaluates ok (at least it does in my M15). It shows in red because the result is too large to display. However, the result can be used in further expressions below. The final expression works also, as long as you don't insist on a symbolic result - see attached. Do you really need all those symbolic solutions? Wouldn't numerical results be adequate?

Alan

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ptc-45285571-VisitorAuthor
1-Visitor
April 3, 2012

Thank you very much!!!

Am I right when I assume that you defined a range for "ϕr" and an "resolution" for this range.

And because of this the calculation changes from symbolic to numerical?

Can you please explain what the steps, which are not evaluated, under the heading are for?

Concerning to your question if a numerical result would be adequate.

It is no problem, because if the "resolution" is high enough the result should be exact enough.

A
AlanStevens19-Tanzanite
19-Tanzanite
April 4, 2012

Thomas Egger wrote:

Am I right when I assume that you defined a range for "ϕr" and an "resolution" for this range

Yes.

And because of this the calculation changes from symbolic to numerical?

Partly. A numerical value is calculated at every value of "ϕr" using the symbolic solution.(I think!).

Can you please explain what the steps, which are not evaluated, under the heading are for?

These represent a purely numerical method of solving your equation (the one immediately preceding the disabled solve block). I thought at first that your symbolic solution was taking too long so I produced a numerical version. However, I then returned to your version as you seemed to be keen on having a symbolic solution (If you enable the numerical version you should find it is much faster than the symbolic one).

Alan

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