Kronecker product

[Juliet Hannah]

I am looking for suggestions on how to write the Kronecker product
(direct product). I came across this online:

\def\kronecker{\raisebox{1pt}{\:\otimes\:}},

which is used as: $I_a \kronecker I_n$

however, this gives me some warnings (but eventually works).

The warning is:

<inserted text>
$
l.60 $I_a \kronecker
I_n$
?

Perhaps I am using this incorrectly. I am using WinEdt. Any suggestions?

Thanks,

Juliet

[Prabir Barooah]

I use \otimes, which produces the standard notation for Kronecker
product. Doesn't it work for you?

[Werner Grundlingh]

Understandably you want \otimes raised 1pt, because it seems too low/
close to the baseline. However, using \raisebox{...}{...} forces the
second required argument to be in text mode (as opposed to math mode).
That why LaTeX complains and requires the insertion of $ somewhere...
To rectify the problem, redefine your \kronecker as such:
\def\kronecker{\raisebox{1pt}{\ensuremath{\:\otimes\:}}}
(you could also just use $...$ instead of \ensuremath{...}) or, in
"standard" LaTeX (as opposed to plain TeX):
\newcommand{\kronecker}{\raisebox{1pt}{\ensuremath{\:\otimes\:}}}

Werner