Latex: how to use conditional compilation

If you want to use condition to control your texts, better to use \ifthenelse.
Usage in pre-docu:
\usepackage{ifthen}
\newboolean{yourBoolVar}
\setboolean{yourBoolVar}{boolval} % boolvar=true or false

Usage in main body:
\ifthenelse {\boolean{yourBoolVar}}
{if true, go this code} {if false, go this}

Linux:compress: restrictions about zipped tar files

From the tar's user guide:
Notice also, that there are several restrictions on operations on compressed archives. First of all, compressed archives cannot be modified, i.e., you cannot update (--update (-u)) them or delete (--delete) members from them. Likewise, you cannot append another tar archive to a compressed archive using --append (-r)). Secondly, multi-volume archives cannot be compressed.

Linux:software: How to merge multiple pdf files into one

Use the command in Linux to merge some PDF files into one:

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=firstANDsecond.pdf -dBATCH first.pdf second.pdf

Use it, you have two packages installed in your system

Link: Ghostscript download
Link: PDFtk download

For more information, see the reference link: http://www.newlinuxuser.com/merge-multiple-pdfs-into-one-file/

Linux: alias: shell: define your alias in Linux

Except /etc/profile, ~/.bashrc and ~/.bash_profile, you can add alias into the file:

/etc/profile.d/alias.sh (or alias.csh for c shell)

This file is effective for all users like /etc/profile.

Software: root: tmva: how to install it...

TMVA is a Toolkit for Multivariate Data Analysis with ROOT.
web page: http://tmva.sourceforge.net/
After compiling and before running your code/macros, please make sure your lib is loaded!

Software:programming: how to use auto-complete in xemacs

If you are programming, it will be very convenient to ask your editor to auto-complete words for you! Time-saving! In xemacs (I didn't try it in emacs), you could use shortcut: alt+/