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I want to calculate the eigenvalues form the very huge sparse mass and stiffness matrix.

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HIMANSHU
HIMANSHU 2024-6-20
评论： HIMANSHU 2024-6-24
I have mass and stiffness matrix in sparse format since the size of the matrix is too big.
I want to claculate the eigenvalues from them in the sparse format only. How to do so?

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Aquatris
Aquatris 2024-6-20
编辑：Aquatris 2024-6-20
Ran in:
If eig() function is taking too long, you can use eigs() function.
Example from mathworks eigs() site:
A = delsq(numgrid('C',15));
size(A)
ans = 1x2
139 139
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eigs(A)' % by default 6 largest eigenvalues
ans = 1x6
7.8666 7.7324 7.6531 7.5213 7.4480 7.3517
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eigs(A,20)' % optional argument to define how many eigenvalues you want
ans = 1x20
7.8666 7.7324 7.6531 7.5213 7.4480 7.3517 7.2848 7.1478 7.1093 7.0644 6.9295 6.8257 6.7737 6.7395 6.6472 6.5914 6.4252 6.4118 6.3598 6.3196
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eigs(A,5,'smallestabs')' % optional argument to get the smallest eigenvalues instead
ans = 1x5
0.1334 0.2676 0.3469 0.4787 0.5520
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