Re: Sage
Indeed. I use Matlab extensively in my day-to-day work (research in computational neuroscience) and while it may well be "bad" in any number of senses (e.g. their bolt-on attempt at OO is horrendous), it is nonetheless fabulously flexible and easily refactorable, which is exactly what you want from a research perspective. Maybe best think of it as a scriptable wrapper for Fortran...
My language of choice would probably be Python, but although it is gaining ground in my field, Matlab, unfortunately, remains a de-facto standard.
Aside: I once went for a job interview which included a programming test in R, which I tried to learn in a week. I rather liked R, which seemed extremely flexible, powerful and well thought out, but the learning curve was precipitous to say the least... I never got the job (and as it happened the company folded within months).
Biting the hand that feeds IT
