These are the packages that would be merged, in reverse order:

Calculating dependencies  ..... done!
[ebuild  N     ] sci-physics/root-6.04.06:0/6.04.06::gentoo  USE="X math memstat opengl openmp ssl tiff -R -afs -avahi -doc -emacs -examples -fftw -fits -gdml -geocad -graphviz -http -kerberos -ldap -mpi -mysql -odbc -oracle -postgres (-prefix) -pythia6 -pythia8 -python -qt4 -shadow -sqlite -table -xinetd -xml -xrootd" PYTHON_TARGETS="python2_7" 96,857 KiB
[ebuild  N     ]  media-libs/ftgl-2.1.3_rc5::gentoo  USE="-static-libs" 692 KiB
[ebuild  N     ]  x11-libs/gl2ps-1.3.8::gentoo  USE="zlib -doc -png" 290 KiB
[ebuild  N     ]  sys-devel/clang-3.7.1-r100:0/3.7::gentoo  USE="multitarget static-analyzer -debug -python" ABI_X86="(64) -32 (-x32)" 0 KiB
[ebuild   R    ]   sys-devel/llvm-3.7.1:0/3.7.1::gentoo  USE="clang* libffi multitarget ncurses static-analyzer -debug -doc -gold -libedit -lldb -ocaml -python {-test} -xml" ABI_X86="32 (64) (-x32)" PYTHON_TARGETS="python2_7" VIDEO_CARDS="-radeon" 10,323 KiB
[ebuild  N     ]  media-libs/libafterimage-1.20::gentoo  USE="gif jpeg nls png tiff -examples -static-libs -svg -truetype" CPU_FLAGS_X86="mmx" 994 KiB
[ebuild  N     ]  sci-libs/gsl-2.1:0/19::gentoo  USE="-cblas-external -static-libs" 3,738 KiB
[ebuild  N     ]  x11-libs/libXpm-3.5.11::gentoo  USE="-static-libs" ABI_X86="(64) -32 (-x32)" 0 KiB
[nomerge       ] sci-libs/gsl-2.1:0/19::gentoo  USE="-cblas-external -static-libs"
[ebuild  N     ]  app-eselect/eselect-cblas-0.1::gentoo  0 KiB
[nomerge       ] sci-physics/root-6.04.06:0/6.04.06::gentoo  USE="X math memstat opengl openmp ssl tiff -R -afs -avahi -doc -emacs -examples -fftw -fits -gdml -geocad -graphviz -http -kerberos -ldap -mpi -mysql -odbc -oracle -postgres (-prefix) -pythia6 -pythia8 -python -qt4 -shadow -sqlite -table -xinetd -xml -xrootd" PYTHON_TARGETS="python2_7"
[ebuild  N     ]  virtual/fortran-0::gentoo  USE="openmp" 0 KiB
[ebuild  N     ]  sci-mathematics/unuran-1.8.1::gentoo  USE="rngstreams -doc -examples -gsl -prng -static-libs" 4,307 KiB
[ebuild  N     ]   sci-mathematics/rngstreams-1.0.1::gentoo  USE="-doc -examples -static-libs" 491 KiB
[ebuild  N     ]  dev-lang/cfortran-4.4-r3::gentoo  USE="-examples" 140 KiB

Total: 13 packages (12 new, 1 reinstall), Size of downloads: 117,827 KiB