# 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?

This question is about conventions, and it will differ from field to field. You should use the conventions of your field.

Otherwise, the standard ISO 80000-2 identifies notation for scalars, vectors, matrices, tensors, and more. Symbols for tensors are in sans-serif bold italic. The isomath package implements this in LaTeX.

• Thank you so much for your answer, Arya! I checked the materials you mentioned, and it seems the symbols of matrix(2-15.1) and tensor(2-17.19) are the same: both are sans-serif bold italic with a capital case. Thanks again! – Nick Chen Jun 14 at 3:10
• The matrix notation has serifs. The tensors don’t. – Arya McCarthy Jun 14 at 3:14
• Sorry I didn't notice that difference! Thank you so much for pointing it out. Problem solved! – Nick Chen Jun 14 at 3:45
• +1 for isomath, great little package – Firebug Jun 14 at 17:21