How to Running two NS2 versions on single OS

he different versions of NS-2 can be installed on a computer by below given steps:

1. Install one version of NS-2 and create a .bash_profile1 for updating the environment variable

2. Install another version of NS-2 and create a .bash_profile2 for updating the environment   variable

3. Then to switch from one version to another version use following commands

    a) source ~/.bash_profile1

    b) ./configure

    c) make install

    d) make clean

    e) make

So, to switch the library of command you need to appropriate bash_profile file as source for environment variables.