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sfan1-Visitor
1-Visitor
November 8, 2015
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Find the eigenvalues

  • November 8, 2015
  • 1 reply
  • 2972 views

Hi, everyone,

Is there a way to find the value of lambda using the eigenvals function in Mathcad?

What have I done wrong such that it cannot return to the numerical solution such as the polyroots results?

Capture.JPG

For this simple question, the polyroots function is acceptable,

but I assume using the eigenvals be more convenience when there are much bigger matrix that needs programming.

BTW, is there any recommendations for the method to use, when say there is a N Degree of Freedom vibration system, that N is the input of a function, that returns to the eigenvalues and eigenvectors. Is the built in Eigenvals function convenient to use?

Thank you!

Shawn

Best answer by Werner_E

Is there a way to find the value of lambda

Yo are not telling us, which equation you want to be solved for lambda?

It seems that you are searching for values of lambda which make the determinant of C to zero.

So the most direct way would be

What have I done wrong such that it cannot return to the numerical solution such as the polyroots results?

??? I have no clue what you are talking about. Where did you expect to get those numerical values? BTW, I am only talking about the picture you sent, as my P3 version can't read P3.1 files.

Is there a way to find the value of lambda using the eigenvals function in Mathcad?

Yes, see below. If the determinant of C is zero, one of the eigenvalues has to be zero. But I see no reason why you would use this method.

If you really want to use "polyroots", you could do it a bit more convenient that way:

WE

1 reply

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Werner_E25-Diamond IAnswer
25-Diamond I
November 8, 2015

Is there a way to find the value of lambda

Yo are not telling us, which equation you want to be solved for lambda?

It seems that you are searching for values of lambda which make the determinant of C to zero.

So the most direct way would be

What have I done wrong such that it cannot return to the numerical solution such as the polyroots results?

??? I have no clue what you are talking about. Where did you expect to get those numerical values? BTW, I am only talking about the picture you sent, as my P3 version can't read P3.1 files.

Is there a way to find the value of lambda using the eigenvals function in Mathcad?

Yes, see below. If the determinant of C is zero, one of the eigenvalues has to be zero. But I see no reason why you would use this method.

If you really want to use "polyroots", you could do it a bit more convenient that way:

WE

S
sfan1-VisitorAuthor
1-Visitor
November 9, 2015

Hi, Werner,

Thank you so much for your explanation.

I bought the student version of 3.1 and it is awful that 3 cannot support 3.1 files as they have the same format.

Is there a way to have 3.1 export the 3.0 version of file?

Capture.JPG

I just figure out that maybe this way is more efficient.

Best

Shawn

W
Werner_E25-Diamond I
25-Diamond I
November 9, 2015

I bought the student version of 3.1 and it is awful that 3 cannot support 3.1 files as they have the same format.

Is there a way to have 3.1 export the 3.0 version of file?

Unfortunately no - PTC had decided that there should be no way back and no compatibility - ridiculous!

WE

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