A vector is interpreted as a one-column matrix (a column vector)
To become a one-row matrices, use transpose to turn a column vector into a row vector.
<MATH> \begin{array}{c} \text{Suppose } {\bf b} = [1, 2, 3] \\ [1,2,3] * A = [1 2 3] * \begin{bmatrix} & & \\ & \large{A} & \\ & & & \end{bmatrix} = {\bf b}^T A \end{array} </MATH>