Find the eigenvalues

[sfan]

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?

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

[Werner_E · Accepted solution]

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

[sfan]

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?

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

Best

Shawn

[Werner_E]

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

[StuartBruff]

Werner Exinger wrote:

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

To be fair to PTC, Mathcad has rarely been forwards compatible.   I don't recall being able to read, for example, M12..M15 worksheets in M11, or even M13 worksheets in M12.   M14 reads M15 in part because M15 seems to be a version of M14 under the hood.   The Collaboratory and Community have seen many requests to save worksheets in earlier versions.

However, Mathcad Version N did usually have the ability to save back several versions, and this is the real source of the problem - there's nothing anyone can do to make a worksheet available to earlier versions.   In my workplace, we have/had people working on different versions of Mathcad because, for example, version N might be cleared by IT to run on a given system (Win XP) but version N+m wouldn't, even though it was in use elsewhere.  Or it may be that differences in behaviour between versions mean that somebody prefers to work in M13 rather than M15 (eg, Maple rather than MuPad).  Or, of course, have to work in M15 because Prime doesn't have the features they want.

Stuart

[Werner_E]

To be fair to PTC, Mathcad has rarely been forwards compatible.

Thats true for most other software, too, and I wouldn't complain about a software not being foreward compatible (even though I would expect forward compatibility in subversions - 3.0 shoud be able to read 3.1 files):

However, Mathcad Version N did usually have the ability to save back several versions,

Exactly thats the main point! In MC15 we can save back up to MC11 format and as we can install MC11 parallel with MC15, we can even save back to much older formats then using MC11.

Its natural for newer versions of a software (apart from some CAD progs) to be able to save back in older formats, maybe losing a feature or two in doing so.

Microsoft even provided an automatic, transparent converter, when the introduced the new file format with M$ Word 2007. Thus making Word 2003 forward compatible without any hassle.

The continuous change of file formats (keeping the very same extension *.mcdx) even when introducing subversions and not providing at least a way to save back in older formats really is a PITA.

Werner

[sfan]

My bundled pack included M15 and Prime 3.1. So I can also install the two on my PC in parallel.

However, I think the prime file should be able to support different versions, as they all have the same format.

My school computer cluster has the 3.0 version, maybe next time I can go there and post the question files,

otherwise I will try to include a screenshot that is comprehensive enough.

Anyway, thank you guys for your patience and help with me, always!

Shawn