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

Calculating dependencies ... done!
Dependency resolution took 1.01 s (backtrack: 0/20).

[ebuild  N     ] sci-libs/atlas-3.11.41::gentoo  USE="lapack threads -doc -fortran -generic -static-libs" 6489 KiB
[ebuild  N     ] sci-libs/fftw-3.3.10-r1:3.0/3::gentoo  USE="openmp threads -doc -fortran -mpi -test (-zbus)" CPU_FLAGS_X86="avx avx2 fma3 sse sse2 -fma4" 4047 KiB
[ebuild  N     ] sci-astronomy/psfex-3.17.1::gentoo  USE="threads -doc -plplot" 2311 KiB

Total: 3 packages (3 new), Size of downloads: 12847 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by sci-astronomy/psfex-3.17.1::gentoo
# required by =sci-astronomy/psfex-3.17.1 (argument)
>=sci-libs/atlas-3.11.41 lapack