If you're a Matlab user you may be interested in Scilab. While the user interface is not as polished as that of Matlab, it is a first-rate numerical computational tool that, almost certainly, will allow you to do for free in Scilab what you've been doing for a price (thousands of American dollars) in Matlab. You also don't have to worry about ridiculous licensing and installation procedures. If you're a college student, you can buy student editions of Matlab for relatively little money (approx $100?) but consider the open source option too. The reason MathWorks sells cheaply to students and faculty is to grow demand at work when the students move onto gainful employment. (Yes, eventually you will graduate, I know it doesn't seem that way right now!)
Scilab is open source and binaries are available for download for free unices and for Windows. Source code is also available, of course.