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Matlab (calculate natural frequencies using eig function)

  1. Dec 17, 2015 #1
    1. The problem statement, all variables and given/known data
    Determine the corresponding natural frequencies
    M = [1 0 0 0;0 1 0 0;0 0 1 0;0 0 0 1];
    C = [2 0 0 0;0 0 0 0;0 0 0 0; 0 0 0 0];
    K = [10 -5 0 0;-5 10 -5 0;0 -5 10 -5;0 0 -5 10];
    2. Relevant equations
    A = [zeros (4) eye(4); -M/K -M/C]
    [V,D] = eig(A)

    3. The attempt at a solution
    just need help on A = [zeros (4) eye(4); -M/K -M/C].
    -M/C =
    NaN NaN NaN NaN
    NaN NaN NaN NaN
    NaN NaN NaN NaN
    NaN NaN NaN -Inf

    I also try with -inv(M*C)
    -Inf -Inf -Inf -Inf
    -Inf -Inf -Inf -Inf
    -Inf -Inf -Inf -Inf
    -Inf -Inf -Inf -Inf

    This matrix caused the [V,D] = eig(A) cannot work.
    Any step that i missed up?
     
  2. jcsd
  3. Dec 17, 2015 #2

    DrClaude

    User Avatar

    Staff: Mentor

    Is that really the complete problem your were given?
     
  4. Dec 17, 2015 #3
    For a system with the mass, damping, stiffness matrices given as below:
    M = [1 0 0 0;0 1 0 0;0 0 1 0;0 0 0 1];
    C = [2 0 0 0;0 0 0 0;0 0 0 0; 0 0 0 0];
    K = [10 -5 0 0;-5 10 -5 0;0 -5 10 -5;0 0 -5 10];
    Determine the corresponding natural frequencies by using Matlab eig function.
     
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