> Fabrice Couvreur <mailto:fabrice1.couvreur@gmail.com>
> 17. April 2016 um 11:16
> Hello,
> I compiled this file with a strange exit for mathematical formula.
What do you mean with "strange exit"?
> What's missing in my file ?
You get the necessary font when you use the "--fonts=mathdesign" for 
first-setup, e.g.

     sh first-setup.sh --fonts=mathdesign

and your example can be reduced to (you can drop encoding=...)

%% begin example
\loadtypescriptfile[mathdesign]

\definetypeface[mainface][rm][serif][palatino] [default]
\definetypeface[mainface][ss][sans] [helvetica][default][rscale=auto]
\definetypeface[mainface][mm][math] [utopia]   [default][rscale=auto]

\setupbodyfont[mainface,12pt]

\starttext

\input knuth

\startformula
    f(x) = \sum_{i=1}^n a_i x^i
\stopformula

\stoptext
%% end example

There are a few mistakes in the output because the mapping from glyphs 
to unciode
values for the math font has to be improved.

Wolfgang