My eig function worked once and then broke
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Hello everyone,
I am currently trying to solve a vibrant system, and I need its eigenvalues and eigenvectors. I so used the eig() function, as following:
[EigVec, EigVal] = eig(K\M, 'vector') % K the stiffness matrix, M the mass matrix
I tried it once and got the exact right results. I modified some values in the mass matrix and now this line isn't working anymore. I get the following error:
Error using sym/eig
Too many input arguments.
Error in Homework2 (line 347)
[EigVect, EigVal] = eig(K\M, 'vector');
I also tried:
[EigVec, EigVal] = eig(K\M)
And now I get absurd values.
Any ideas of what happened?
1 个评论
Christine Tobler
2022-4-20
It sounds like originally your matrices didn't contain symbolic variables, so the eig command accepted the 'vector' option (eig for symbolic variables doesn't accept any option strings). Then you changed M so that it's now a symbolic variable - and those have quite different behavior, since it's not numerical calculation anymore but symbolic.
Can't really tell more since I don't know what you mean by absurd values, or what you expect in terms of symbolic calculation (for example, is M a specific number just in stored symbolically, or does it contain symbolic unknowns)?
We really need reproduction steps of what K and M are, and what you're hoping to compute, to help any more.
采纳的回答
Bruno Luong
2022-4-20
0 个投票
Don't use symbolic variable to build your matrices.
2 个评论
Benjamin KOENIG
2022-4-20
Bruno Luong
2022-4-20
编辑：Bruno Luong
2022-4-20
"Error using sym/eig"
implies you have symbolic variable.
If
eig(K\M)
returns "absurd" result perhaps your matrices input is not correct ("I modified some values in the mass matrix" but what?) . But you don't tell us what ther are and why it is absurd. The only absurd thing to me is that you expect useful help from so little information.
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