Update.
I moved the file to the wrong bin folder i think.
after moving it to /usr/local/bin i no longer get the message that cortex_var_31_c1 can't be found.
however i now get a new message:
cortex_var_31_c1: error while loading shared libraries: libgsl.so.19: cannot open shared object file: No such file or directory
I looked in the gsl-1.15 file.
used ( sudo) ./configure and afterwards used (sudo) make.
however then i get the next error message:
./rng.texi:1411: warning: @itemize has text but no @item
./qrng.texi:168: warning: @itemize has text but no @item
./multimin.texi:143: must be after `@deftypefun' to use `@deftypefunx'
./bspline.texi:255: warning: @itemize has text but no @item
./bspline.texi:263: warning: @itemize has text but no @item
make[2]: *** [
gsl-ref.info] Error 1
make[2]: Leaving directory `/media/STUDENT_FS1/CORTEX_v1.0.5.21/libs/gsl-1.15/doc'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/media/STUDENT_FS1/CORTEX_v1.0.5.21/libs/gsl-1.15'
make: *** [all] Error 2