Matrix algebra

I am currenly reading about the fisher linera discriminant (Bishop pattern
recognition p 189 ) . w is an optimal projection vector that is esitmated
by:

w = inv(Sw)*(m1-m2)

Sw is a n*n covarians matrix and m1, m2 are mean 1*n (row) vectors. But how
is that product legal? As I understand matrix/vector products are only
allowed if they respect:

(m*n) * (n*k) = m*k

but w is on the form:

(n*n) * (1*n)

which is illegal.


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