Malfunction to my matrix calculation

Below here, I want to calculate the matrix of X.

From what I understand, K is a 4x4 matrix, and F is a 1x4 matrix.

In order to get X, I have to transpose my martix F, so it can be a 4x1 matrix.

Therefore, X should be a 4x1 matrix.

The problem here is what I get instead is a 4x4 matrix, which can be shown in the second picture below.

Is there a typo problem or something that I didn't notice about the code?

Answer 1

[James Tursa]

K .* F (with the dot) does element-wise multiplication with implicit array expansion if the variables are different sizes, thus the 4x4 result.

K * F (without the dot) does matrix multiply and will get a 4x1 result.

E.g.,

K = rand(4,4); % 4x4
F = rand(1,4); % 1x4
K = inv(K); % 4x4
F = F'; % 4x1
K .* F % the 4x1 is implicitly expanded to 4x4 for this element-wise operation

ans = 4×4

-0.2635 0.3232 0.0993 -0.4084 -0.6048 -0.5805 1.1160 0.2753 3.4958 -2.9911 -2.9084 6.3079 -0.1182 0.2026 0.2726 -0.5389

K * F % a normal matrix multiply

ans = 4×1

1.2976 1.6914 -2.6004 1.0808