# How to express the notion of a vector, where every element inside is matrix?

I met a question when I tried to express a vector, where every element inside is a matrix. We know the notion usually works like this:

• scalar: $$a$$
• vector: $$\boldsymbol{a}$$
• matrix: $$\boldsymbol A$$
• vector (elements inside are vector): $$\boldsymbol{A} = [\boldsymbol{a}_1, \boldsymbol{a} _2, \boldsymbol{a} _3]$$

What if I want to express a vector (or tensor) where the elements are matrices, like the following:

• vector (elements inside are vector): $$? = [\boldsymbol{A}_1, \boldsymbol{A} _2, \boldsymbol{A} _3]$$

Should I still use $$\boldsymbol A$$, Or is there a formal expression?