# Second order ODE application question

by cue928
Tags: stiffness matrix
 P: 131 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?
 PF Patron HW Helper Sci Advisor Thanks P: 25,505 hi cue928! not really my subject, so i'm going to risk asking what could be a really dumb question … if there's only two degrees of freedom, how come there's three parameters? (and your general formula doesn't have rows summing to 0 … maybe these are just the top triangle of a 3x3 matrix?)
 P: 131 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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