# [NTG-context] how to use \dimexpr and fractional values

Thomas A. Schmitz thomas.schmitz at uni-bonn.de
Fri Jun 28 08:54:22 CEST 2013

Hi all,

long story short: I want to calculate a width or height from user input,
which is in the form "0.x" (as in "0.3\textwidth") since I want to use
that number differently in different circumstances. Problem is that
\dimexpr doesn't like decimal values. Example (uncomment second
\externalfigure to see the problem):

\starttext

\def\myfactor{0.3}

\externalfigure[mill][height=\myfactor\textwidth]

%\externalfigure[mill][height=\dimexpr10cm*\myfactor\relax]

\stoptext

(silly, but shows my problem). How can I obtain an image of height
"0.3*10cm" from my \myfactor macro? I tried to get my head around
\numexpr etc. in the etex manual, but couldn't really figure out what to do.

Thanks, and all best

Thomas