ngspice

USE flags

• debug - Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces
• deprecated - Build old and deprecated apps
• doc - Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
• examples - Install examples, usually source code
• fftw - Use FFTW library for computing Fourier transforms
• openmp - Build support for the OpenMP (support parallel computing), requires >=sys-devel/gcc-4.2 built with USE="openmp"
• readline - Enable support for libreadline, a GNU line-editing library that almost everyone wants
• shared - Build ngspice as a shared library
• tcl - Add support the Tcl language
• test - Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
• X - Add support for X11