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polyeig gives different eigen values for the same matrices.

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Dhruv Thakkar
Dhruv Thakkar 2019-12-5
编辑： Walter Roberson 2019-12-5
I am trying to find eigen value for a system with the Global mass, stiffness and damping matrix. There are two sets of matrices with one set name as:
GLK - Global stiffness matrix
GLC - Global damping matrix
GLM - Global mass matrix
and the other set as
glk - Global stiffness matrix
gld - Global damping matrix
glm - Global mass matrix.
In spite of the fact that both set of matrices are exactly the same, polyeig returns different eigen values.
In the matlab file that I have attached a and b are:
a = polyeig(GLK,GLC,GLM);
b = polyeig(glk,gld,glm);

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Walter Roberson
Walter Roberson 2019-12-5
编辑：Walter Roberson 2019-12-5
In spite of the fact that both set of matrices are exactly the same
But they are not.
>> isequal(GLC,gld)
ans =
logical
0
>> max(max(GLC-gld))
ans =
0.224105817267403
>> min(min(GLC-gld))
ans =
-0.224105817267403
I find it odd that for the two that are exactly the same, that the names are upper/lower case of each other, and that for the ones that differ, the names differ (GLC vs gld) and I have to wonder if you have accidently used the wrong matrix.

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