# How to solve det(s^2*M+s*C(s)+K)=0 for s as fast as posible

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Rodrigo Moscoso Cires 2018 年 7 月 1 日

Hello, I want to solve the equation:
det(s^2*M+s*C(s)+K)=0
for s. In this equation M, C and K are big (at least 100x100), sparse matrices and C depends on s (it has the term (50/(s+50)) in it). Is there a faster way to solve this besides the following procedure?:
1. using the symbolic variable "s"
2. finding the determinant with the command det(s^2*M+s*C(s)+K)
3. solve the equation using the command solve(det(s^2*M+s*C(s)+K==0,s) and then
4. vpa(solve(det(s^2*M+s*C(s)+K)==0,s))
I tried to use polyeig(s^2*M+s*C(s)+K) as an alternative, but it just solves the equation for a constant C and not for C(s).

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### 回答 (1 件)

Sergey Kasyanov 2018 年 7 月 6 日
You can try to use that code from there:
A=GaussElimination(s^2*M+s*C+K,'');
[~,d]=numden(A(end,end));
Solution=solve(d,s);
You must define C as symbolic matrix. Also I don't ensure that it will be work right, but you can rewrite GaussElimination() for your purpose (function GaussElimination() was wrote fast and for solving another narrow problem, but sometimes I use it for determinant calculation).

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