# \hdotsfor{''n''} []

Hello,
I am trying to spread the ellipsis over many columns of a matrix... lyx
shouts:
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., \hobx'), type I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

Is there a specific miktex (mpm.exe) package I need to see installed?

Rds,