Second order ODE application question

  1. We are doing mass spring problems that stem from second order ODE's. I think my lack of linear algebra is hurting me once again in this section so any help would be greatly appreciated.
    We are using a stiffness matrix of K = [ -(k1+k2), k2 (row 2) k2, -(k2+k3)]
    Our first problem has the following values: m1=m2=1; k1=0, k2=2, k3=0
    Setting up the stiffness matrix I got the following:
    -2 2
    2 -2
    So this is my first stopping point: I thought you were supposed to then take the inverse of that but can you do that with a matrix that has a determinant of zero?
  2. jcsd
  3. tiny-tim

    tiny-tim 26,016
    Science Advisor
    Homework Helper

    hi cue928! :smile:

    not really my subject, so i'm going to risk asking what could be a really dumb question :redface:

    if there's only two degrees of freedom, how come there's three parameters? :confused:

    (and your general formula doesn't have rows summing to 0 …

    maybe these are just the top triangle of a 3x3 matrix?)​
  4. I don't know how to answer that. Since there is a zero value for two of them, maybe that has something to do with it? I honestly don't know.
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