# How do I do simultaneous equations with unknown variables?

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Gowutheyaan Ratnasingam 2019 年 11 月 18 日

I have worked out a global stiffness matrix and the global force vector. After this I need to do an equation [K][q] = {f}
Where {q} =
q1
q2
q3
Where q1 is equal to zero, and the other two are values to be found, how do I find these values? When I try, Matlab keeps on saying q2 etc. are undefined. It also doesn't seem to accept F = K*Q for some reason too
Code so far:
Edof = [1 1 2; 2 2 3];
K = zeros (3,3);
F = zeros (3,1);
F (2) = 4;
F (3) = 2;
k1 = 60;
k2 = 30;
Ke1 = [k1 -k1; -k1 k1];
Ke2 = [k2 -k2; -k2 k2];
K(1:2,1:2) = Ke1;
K(2:3,2:3) = K(2:3,2:3) + Ke2;

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### 回答 (1 件)

Siriniharika Katukam 2019 年 11 月 21 日
Hi
"linsolve" does the solving in your case.
Pass K and f as inputs to linsolve.

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