how can i install third party software like matlab ,multisim

please give me a good solution

Matlab usually has two bits to it Matlab its self which a text based product and simulink which is a graphical product. I don't think either are available for Linux.

However there is a product that's very similar to matlab called octave. Its so close that almost all "m" files work without modification.

A program similar to simulink is scilab. It has much of the same functionality but uses it own file format
so you cant share projects with simulink

both are in the repositories

There are a number of pspice packages available but my personal preference is LTSpice this is a windows program but runs well under Wine. It can be downloaded from here

http://www.linear.com/designtools/software/

Matlab (as well as simulink) is originally (and still is) Unix based. It runs under linux, and you can install it from any matlab CD. It has both the GUI and command line components.

That said, I recommend scilab over matlab, as it is far far easier to install -- scilab has no licence server. Scilab also has a graphical interface, and is a very similar syntax to matlab, but not quite drop-in replacement (some function names and variable orderings change).