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
K * F % a normal matrix multiply
