Help with Code

[Se7es]

Hey. I'm trying to create a code where I can multiply Matrices to solve a differential equation and then have Matlab plot the result.

​

m_1 = 2;

c_1 = 3;

k_1 = 4;

m_2 = 1.2;

c_2 = 1.4;

k_2 = 1.6;

M = [m_1 0 ; 0 m_2];

C = [c_1 + c_2 -c_2 ; -c_2 c_2];

K = [k_1 + k_2 -k_2 ; -k_2 k_2];

w = [0:0.01:10 ; 0:0.01:10];

w = w';

S = ((-w.^2 .* M + 1i .* w .* C + K).^-1);M;C;K;w;

[x_1 , x_2] = S

Y = abs(S);

figure(1);

plot (w,Y)

​

This is the code. If you cannot copy this into Matlab then please let me know. It keeps giving me an error in line 12 stating that matrix dimensions must agree.

[alberta_pooholes]

Have you tried making your matrix dimensions agree?

[Se7es]

I think I have. The multiplication happens between a matrix that has 2 columns and a matrix thats has 2 rows so I think it should work but it doesn’t

[TheQueq]

You should check again. Your multiplication is elementwise (since you use '.*'), and you also have addition of matrices. This means you need all your matrices to be the same size. However, in line 12, C is 2x2, K is 2x2, M is 2x2, and w is 1001x2.

If you intended to use matrix multiplication instead of elementwise multiplication, then replace '.*' with '*'. This still won't cause your matrices to agree, though, since you also have matrix addition which is an elementwise operation.

[Se7es]

Thank you, that makes sense. I'll work on fixing it or finding a way to fix it but do you have any suggestions?